He realized she was crying [ ]what he had sad. 【说一下原因】A,because B,because of C,as D,since

He realized she was crying [ ]what he had sad. 【说一下原因】A,because B,because of C,as D,since
He realized she was crying [ ]what he had sad. 【说一下原因】
A,because B,because of C,as D,since

He realized she was crying [ ]what he had sad. 【说一下原因】A,because B,because of C,as D,since
B what he had sad.做从句,what是连接词,不用because,as ,since ,只能用because of ,让what 引导的从句作介词宾语.

B,because of