We all feel it is Jack as well as his wife that for their son's bad performance at school

问题补充：

We all feel it is Jack as well as his wife that for their sons bad performance at school.

A. are to blame

B. is to the blamed

C. are to be blamed

D. is to blame

答案：

A. are to blame

B. is to the blamed

C. are to be blamed

(答案→)D. is to blame

解析：考查blame用法和主谓一致。固定词组be to blame应受责备。该词组用主动语态表示被动含义。本题的主语是Jack，故使用单数形式。故D正确。句意：我们感觉Jack和他的妻子应该为他们的儿子在学校的糟糕表现负责。