单选题：One of the problems PVTs have is that__________.

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题目类型：单选题
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题目内容：

One of the problems PVTs have is that__________. A．their thermal applications are costly.
B．they are too expensive to afford.
C．theyoccupy too much space.
D．it is hard to fix them on the roof.

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Melting of snow and ice enables sunlight to reach __________

Melting of snow and ice enables sunlight to reach __________A．the exposed ground

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Arctic ice has never been melting so fast in __________

Arctic ice has never been melting so fast in __________A．the exposed ground B．a

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根据以下材料，回答题Why Don't Babies Talk Like Adults?Over the past half-century, scient

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根据以下材料，回答题Around 45% of the UK's carbon dioxide emissions come from the energy

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According to Dr. David Faxon, the self-contained heart is___

According to Dr. David Faxon, the self-contained heart is__________.A．a mileston

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