问题描述：
More than twenty people were believed ______in the air crash.
A.to have been dying B.to have died
C.to die D.to be dying
应该选B.为什么不能选C,
A.to have been dying B.to have died
C.to die D.to be dying
应该选B.为什么不能选C,
问题解答：
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