He realized she was crying what he had sad.A. becauseB. because ofC. asD. since

问题补充：

He realized she was crying what he had sad.

A. because

B. because of

C. as

D. since

答案：

A. because

(答案→)B. because of

C. as

D. since

解析：考查名词性从句。what he had sad是名词性从句，而连词because, as和since

不能引导名词性从句，所以选B，because of，介词of后面引导的是宾语从句。