Who do you think for the failure of their marriage?
A. to blame
B. to be blame
C. is to blame
D. is to be blamed
网友回答
A. to blame
B. to be blame
(答案→)C. is to blame
D. is to be blamed
解析： do you think 为插入语，who is to blame 是句中主干，to blame不定式作表语，用主动表被动。