Pollution is a serious problem. Scientists have some good ways to save it. A. come up wit

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。