The acid rain is one of the chain reactions that ______ by environmental pollution
问题描述：
The acid rain is one of the chain reactions that ______ by environmental pollution
A.is come about
B.is caused
C.are given birth
D.are brought about
为什么选D不选B
答
因为that 后面的内容是修饰 chain reactions,是复数,如果B是 are caused就可以选了.