Airpollutionis________bywastegases

发布时间：2020-07-10 16:24:25

Air pollution is ________ by waste gases of cars.













A.main cause












B.mainly causing











C.main caused











D.mainly caused

网友回答

D解析解析：be caused by意为“被引起”。mainly是副词，修饰动词caused。
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