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
网友回答
A. must be sent
B. will be sent
C. are sent
(答案→)D. be sent
解析：考查虚拟语气。 It is essential that + 从句，从句用should + V原形的虚拟语气，should可以省略，选D。