问题
选择题
Scientists have been worried for years about the ________ of air pollution on the earth's natural
conditions. [ ]
A. effect
B. reason
C. account
D. cause
答案
答案：A
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Scientists have been worried for years about the ________ of air pollution on the earth's natural
conditions. [ ]
A. effect
B. reason
C. account
D. cause
答案：A
