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Oceanologist:?Recently an unprecedented number of dead dolphins washed ashore along the mid-Atlantic coast. In the blood of over half of the dolphins, marine biologists discovered a brevotoxin that had been emitted by the alga?Ptychodiscus brevis,?in what is known as a red tide. Additionally, polychlorinated biphenyls (PCB), a toxic industrial compound, was also found in the dolphin's blood. A reasonable conclusion, and indeed one many have drawn, is that the dolphins were simply victims of the brevotoxin. Nonetheless, brevotoxins, by themselves, are not lethal to dolphins, though they do tax the dolphins system. Furthermore, most dolphins have some accumulated brevotoxins in their blood without suffering any ill health effects. Therefore, the brevotoxins alone cannot explain the mass beaching of dead dolphins.

第1题

Which of the following, if true, does most to help explain the oceanologist's doubt that the brevotoxins were the primary cause of the dolphins washing upon shore?

A.Most stricken dolphins that wash upon shore, whether or not they eventually die, tend to do so in the Gulf of Mexico.
B.Shortly before the dolphins washed ashore, a major oil spill not only caused algae to release brevotoxins but also released an array of deleterious industrious pollutants, including PCB.
C.While PCB can cause metabolic imbalances in dolphins so that they stop eating prematurely, the dose of PCB a dolphin encounters in the wild is unlikely to pose a lethal threat to a dolphin.
D.Scientists, near to the site of the beached dolphins, discovered a group of beach sea otters exhibiting similar symptoms as the dolphins.
E.PCB and brevotoxins exercise different effects on an organism, with PCB causing visible lesions.

B显示答案

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