请教prep一道语法题

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 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

答案是A。

请教下 that从句可以跨越is signed 修饰agreement么？

另外if the deal were 是否if虚拟语气里不管主语是单数复数都用were而不用was 啊？ 

第一个问题是可以 因为be signed做谓语成分

第二个问题 也对 虚拟中主语单数复数时要用were（包括I、We......）