--What do you think of it?--I think it is a thing of importance that it done soon.A. is B

问题补充：

--What do you think of it?

--I think it is a thing of importance that it done soon.

A. is

B. is to be

C. be

D. to be

答案：

A. is

B. is to be

C. be

(答案→)D. to be

解析：can/could not +have done用于疑问句或否定句时，表示对过去情况的推测.表示不可能作过某事。