Dark matter and dark energy have little effect on conventional matter over familiar distances. Instead, they make their presence known through their prodigious gravitational effects. In tracking them down, therefore, astronomers have had to study gigantic assemblages of matter, extending across spans of millions and billions of light-years. Perhaps the first to take that sweeping viewpoint was the Swiss-American astronomer Fritz Zwicky. In the 1930`s, Zwicky traced the motions of individual galaxies within great clusters of galaxies and made a remarkable discovery: the individual galaxies are moving too fast to be held together in a cluster by the force of gravity exerted by the starry matter visible within them. From his measurements, Zwicky concluded that the great clusters of galaxies must be held together by the gravitational effect of some unseen mass, which he dubbed"dark matter."
It can be inferred from the passage that Zwicky hypothesized the existence of "dark matter" in order to account for
In?Don Giovanni, what is perhaps Mozart`s best-known opera, there exist two distinct endings, a phenomenon not entirely unknown during the composer`s time, but one that invites the obvious question: Why did Mozart decide to include alternate endings for?Don Giovanni, when he did not do the same with his other famous operas,?Die Zauberfl?te?and?Le Nozze di Figaro. Another question, and one not so obvious, is: Why was Mozart himself uncertain as to which of the two endings to choose, as is evidenced in his correspondence with Lorenzo Da Ponte, the opera`s librettist?

A common answer is to treat both these questions as one: Mozart was uncertain as to which ending to provide, so he wrote both endings. Such a reply ignores an important consideration: Why did Mozart decide to provide these specific endings? Libard provides a reasonable answer: The traditional ending-in the sense that it is the one that was popular during the composer`s day, and continues to be so today-is clearly more palatable for audiences. The hero, Don Giovanni, is chided for his libertine ways and then the cast appears in tutti, bellowing a merry chorus as the curtain falls. The audience is left having a light dose of entertainment, which, after all, was the aim of many of the operas of Mozart`s time. Fine, but then what of the tragic ending? Libard-trading the sensible for the pat-offers little more than that such an ending reflects the political climate of the day.

This alternate ending-Don Giovanni is suddenly cast down to Hell, and instead of being redeemed, the hero emerges from the underworld chastened, and the curtain falls-was interpreted by the critics of the day as heavy-handed didacticism. While such a view is not entirely without merit-Mozart ultimately aimed to impart some lesson for his incorrigible Lothario-it still leaves the questioned unanswered as to why two endings, and what exactly did Mozart aim to communicate that could not be housed in a traditional ending.

One answer offered recently by musicologist Gustavo Lucien is that Mozart balked at including a traditional ending, feeling that it was incongruous with the serious tone of most of the opera. Indeed, Don Giovanni falls more under the rubric of opera serie than opera buffo, the latter typically featuring light endings in which the entire cast sings in an upbeat, major key. Da Ponte, however, insisted that forthwith casting Don Giovanni to Hell, and offering him scant opportunity for redemption, would likely leave the audience feeling ambivalent. Such an ending would also suggest that the librettist had been unable to think of a tidy resolution. Da Ponte, then, was not so much against a tragic ending as he was an abrupt tragic ending. Perhaps, even Mozart was unsure of what to do with Don Giovanni once he was in Hell, and may have even been working out a different ending, using the light ending as a stopgap till he achieved such an aim. In that case the fate of Don Giovanni can best be answered by the fact that Mozart-through debts, ill-health, and the composer`s obligation to compose works for his patrons –was unable to return to a work he had tabled.
In the context in which it is used"tabled"most nearly means
The `trophic contamination hypothesis` posits that shorebirds accumulate industrial and urban pollution at stopover sites, toxins that are subsequently released in sudden high doses as fat is burned during migratory flights, disrupting the bird`s ability to make migratory decisions. For example, large contaminant doses might hamper refueling by reducing the satiation signal in shorebirds so that they do not accumulate sufficient fat for migration. A recent study found that, out of those shorebirds that were unable to migrate, some weighed as much as 20% less than the average migrating bird of their species. Whether such findings are a result of shorebirds suffering from trophic contamination, or whether such birds simply cut their migrations short by landing in a foreign ecosystem is unlikely to be resolved until further studies are conducted.?

One promising line of research involves organochlorines, toxins deposited on mudflats in the 1970s and 1980s, now buried by sediments but finally close enough to the surface to be of issue to foraging shorebirds. Organochlorines should be more accessible to long-billed shorebirds that probe deeply for prey than to short-billed species that forage at or near the surface. We predict that an increased number of long-billed shorebirds will either be unable to migrate or will be found along an aberrant flight path.
According to the passage, the author implies that foreign ecosystems have which potential effect on shorebirds?
Vladimir Nabokov, the scientist and the author have been treated as discrete manifestations of a prodigious and probing mind, until now. In her recent biography on Nabokov, Temoshotka makes the bold assertion that these two apparently disparate realms of Nabokov`s polymorphous genius were not so unrelated after all. While Temoshotka cannot be faulted for the boldness of her thesis-Nabokov`s hobby as a lepidopterist (a butterfly collector) and his experience as a novelist informed each other-she fails to make a convincing case. Surely, with enough ingenuity, one can find parallels, as Temoshotka does, between the creative products of Nabokov the naturalist and Nabokov the writer: the intricate butterfly wings that he pored over in his laboratory and the intricate prose that he crafted with sedulous care. But to say the prose of?Lolita?and?Speak Memory?would not have coalesced into their current incarnations had Nabokov`s hobby been, say, lawn tennis is simply reaching too far.
The primary purpose of the passage is to
A construction project has been tasked with building a four-lane road from a remote mountain fortress to a major expressway lying at the base of the mountain. The slope leading to the mountain fortress is so precipitous that the only conceivable way to carry out the project is by building the road downhill, since construction equipment is able to move down, but not up, the steep terrain. The foreman has devised the following solution: dismantle each construction vehicle and tie a part upon the back of a donkey, an animal capable of making the steep ascent. The foreman has at his disposal more than 100 donkeys, each of which is capable of making multiple trips up the mountain.
In order for the foreman`s plan to be successful, which of the following pieces of information is most important?
A company that invests the necessary infrastructure in a large untapped diamond mine can reap as much as 700% profit in the first year.?Some of the largest untapped diamond mines in the world are in the nation of Shagoca.?Therefore, the American company that brokers a deal in the capital Conkin that allows it to put the necessary infrastructure in place at those mines stands to reap tremendous profits.
Which of the following, if true, most helps to explain why American companies are not eager to invest in infrastructure necessary for diamond mining in Shagoca?
The Green Peas Grocery Store in the remote wealthy enclave of Luxville charges more than the Green Peas Grocery Store in Oak City charges for the same items. Clearly, on any given item, the Green Peas grocery franchise is taking advantage of its location in Luxville to reap higher profits on that item.
In evaluating the argument, it would be most useful to compare
Scientists have created double-blind studies so that neither the subjects of the experiment nor scientists know whether a patient is receiving an actual drug or a placebo, which is nothing more than a sugar pill. Essentially, if one knows that one is receiving an actual pill, such knowledge can affect the outcome of a study. A recent study on the effectiveness of the Selective Serotonin Reuptake Inhibitor (SSRI) Freloxamine on depression found that those subjects administered the drug were 15% more likely to have a decrease in symptoms than the control group, which was comprised of those who received a placebo. Since neither group knew which they were receiving, the placebo or the SSRI inhibitor, the observed drop in depression can only be attributed to Freloxamine.
Which of the following, if true, best calls into question the conclusion of the argument?
Galileo's drawings show that he first observed Neptune in 1612, and again in 1613. On both occasions, Galileo mistook Neptune for a fixed star when it appeared very close-in conjunction-to Jupiter in the night sky; hence, he is not credited with Neptune's discovery.

During the period of his first observation, Neptune was stationary in the sky because it had just turned retrograde that very day (retrograde refers to the apparent backward motion created when the orbit of the Earth takes it past an outer planet). Since Neptune was only beginning its yearly retrograde cycle, the motion of the planet was far too slight to be detected with Galileo`s small telescope.
According to the passage, all of the following can account for Galileo`s inability to identify Neptune as a planet EXCEPT?
As to when the first people populated the American subcontinent is hotly debated. Until recently, the Clovis people, based on evidence found in New Mexico, were thought to have been the first to have arrived, some 13,000 years ago. Yet evidence gathered from other sites suggest the Americas had been settled at least 1,000 years prior to the Clovis. The "Clovis first"idea, nonetheless, was treated as gospel, backed by supporters who, at least initially, outright discounted any claims that suggested precedence by non-Clovis people. While such a stance smacked of fanaticism, proponents did have a solid claim: if the Clovis peoples crossed the Bering Strait 13,000 years ago, only after it had become ice-free, how would a people have been able to make a similar trip but over ice?

A recent school of thought, backed by Weber, provides the following answer: pre-Clovis people reached the Americas by relying on a sophisticated maritime culture, which allowed them to take advantage of refugia, or small areas in which aquatic life flourished. Thus they were able to make the long journey by hugging the coast as far south as to what is today British Columbia. Additionally, they were believed to have fashioned a primitive form of crampon so that they would be able to dock in these refugia and avail themselves of the microfauna. Still, such a theory begs the question as to how such a culture developed.

The Solutrean theory has been influential in answering this question, a fact that may seem paradoxical--and startling--to those familiar with its line of reasoning: the Clovis people were actually Solutreans, an ancient seafaring culture along the Iberian peninsula, who had--astoundingly given the time period--crossed into the Americas via the Atlantic ocean. Could not a similar Siberian culture, if not the pre-Clovis themselves, have displayed equal nautical sophistication?

Even if one subscribes to this line of reasoning, the"Clovis first"school still have an objection: proponents of a pre-Clovis people rely solely on the Monte Verde site in Chile, a site so far south that its location begs yet another question: What of the 6,000 miles of coastline between the ice corridor and Monte Verde? Besides remains found in network of caves in Oregon, there has been scant evidence of a pre-Clovis peoples. Nonetheless, Meade and Pizinsky claim that a propitious geologic accident could account for this discrepancy: Monte Verde was located near a peat bog that essentially fossilized the village. Archaeologists uncovered two wooden stakes, which, at one time, were used in twelve huts. Furthermore plant species associated with areas 150 miles away were found, suggesting a trade network. These findings indicate that the Clovis may not have been the first to people the Americas, yet more excavation, both in Monte Verde and along the coast, must be conducted in order to determine the extent of pre-Clovis settlements in the Americas.
If it is true that a trade network between pre-Clovis people had been established, then which of the following could be expected to be found at settlements near Monte Verde?
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