It is essential that these application forms ________ back as early as possible.A.must be sent B.

问题描述:

It is essential that these application forms ________ back as early as possible.A.must be sent B.
It is essential that these application forms ________ back as early as possible.
A.must be sent
B.will be sent
C.are sent
D.be sent
这题选啥啊?

d
should be sent省略should