问题
Pollution is a serious problem. Scientists have _______ some good ways to save it.
A:What
B:Why
C:When
D:How;
B:Why
C:When
D:How;
正确答案是：
同类题型
as he is, Sunyang must have gained ________ richexperience in ________ society as well as sports.
Nothing _____ after the terrible fire caused by someone smoking in bed.[ ]
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”is regarded as a time in their life fun,passion, and imagination seem limitless.