Helen ran out of the classroom in tears, but no one knew( )she was so sad.
A.正确答案Dwhen
B.whether
C.that
D.why
Helen ran out of the classroom in tears, but no one knew( )she was so sad.
Helen ran out of the classroom in tears, but no one knew( )she was so sad.
A.正确答案Dwhen
B.whether
C.that
D.why