It is you as well as your wife that your sons bad performance at school.A. is to be blam

问题补充：

It is you as well as your wife that your sons bad performance at school.

A. is to be blamed for

B. are to be blamed for

C. are to blame for

D. is to blame for

答案：

A. is to be blamed for

B. are to be blamed for

(答案→)C. are to blame for

D. is to blame for

解析：题干中用了强调结构，主语是you，所以谓语要用复数；be to blame是固定句式，用主动形式表示被动意义。