No one knew what because of the thick fog.
A. he had happened
B. had happened to him
C. had he happened
D. has happened to him
网友回答
A. he had happened
(答案→)B. had happened to him
C. had he happened
D. has happened to him
解析：句意：因为大雾，没有人知道他发生了什么事。结合语境可知宾语从句中描述的是过去某时前已经完成的动作，故用过去完成时态。Happen的主语一般为物，happen to sb发生在某人身上，故选B，