求助：管卫东真题中的一道语法题

yiyi1219UID: 161207

Not one of the potential investorsis [U]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 [/U]  not to be concluded. （注：这个是管卫东给出的正确答案）

请问：

1。until从句中,be signed前的should是被省略了呢？还是be signed作后置定语修饰agreement？如果是后者，be是否多余了？

2。划线最后处，the deal were，为什么这里用were？

还是管卫东的答案错了？

gzq1UID: 163083

最好把答案选项贴全.