问题补充:
Pollution is a serious problem. Scientists have some good ways to save it.
A. come up with
B. come on
C. come out
D. come up
答案:
(答案→)A. come up with
B. come on
C. come out
D. come up
解析:句意:污染是个严重的问题,科学家们已经想出了解决的办法。A想出(注意,办法)B继续C出来,出版。D走上前,故选A。