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

请问A中the deal 用were可以吗？不是单数吗？

这是一个虚拟的条件(暗含不希望未来会发生或者未来发生可能性不大的意思).所

以用了were.

not one of +复数名词   谓语动词用单数吗？
这个表达时部分否定吧？为什么不能当做one of +复数名词+复数谓语动词来看呢？

对于of的修饰很迷惑，通常的两个规则one of+n.由n的单复决定谓语动词；the only one of+n.+单数谓语动词，都明白.
但是有的时候the least one/the last one怎么看呢？