There is a crowd of people in front of the house over there. What do you suppose there?A.

问题补充：

There is a crowd of people in front of the house over there. What do you suppose

there?

A. is happened

B. has happened

C. happening

D. to have happened

答案：

A. is happened

(答案→)B. has happened

C. happening

D. to have happened

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