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Photovoltaic cells, which convert light directly to electricity, are safe, have no moving parts, operate at ambient temperature, and last for decades. It would therefore seem that they are one of the more (i)_____ ways to harness the Sun`s energy. However, there is an obvious (ii)_____ widespread application, and that is (iii)_____: electricity generated from photovoltaic cells is getting cheaper, but it still costs more than the going rate in most places.
- inducement to
- danger in
- obstacle to
attractive , obstacle to , expense 显示答案