19.It is necessary that the problem ( ) at once.

问题描述:

19.It is necessary that the problem ( ) at once.
选项:
a、A.should be settle
b、 B.be settled
c、 C.might be settled
d、 D.would be settled

应该是B.
首先句式决定了从句里要用be的原形,而之前有了necessary,就不用再加should/might/would来修饰了.