Pollution is a serious problem. Scientis
题型：选择题
问题：
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
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