Not one of the potential investors is expected to make an offer to buy First Interstate Bank until a merger agreement is signed that includes a provision for penalties if the deal were not to be concluded.

A.        is expected to make an offer to buy First Interstate Bank until a merger agreement is signed that includes a provision for penalties if the deal were
B.        is expected to make an offer for buying First Interstate Bank until they sign a merger agreement including a provision for penalties if the deal was
C.        is expected to make an offer to buy First Interstate Bank until a merger agreement be signed by them with a provision for penalties if the deal were
D.        are expected to make an offer for buying First Interstate Bank until it signs a merger agreement with a provision for penalties included if the deal was
E.        are expected to be making an offer to buy First Interstate Bank until they sign a merger agreement including a provision for penalties if the deal were
   Answer: C
请问为什么要be signed?
谢谢

我不知道怎么解释be signed by，其实我也觉得is signed by貌似也是可以的？但是be signed by我觉得可以做状语所以肯定是可以的。

A 不能用that，that要紧跟在被修饰的名词也就是agreement后面
B not one of  investors后面不是until they sign，至少也应该是个单数的代词
DE的be动词错了，排

于是就是C鸟……