问题补充:
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
答案:
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。