[请教]大全6-20 没有讨论清楚

Seven countries signed a treaty binding each of them to perform specified actions on a certain fixed date, with the actions of each conditional on simultaneous action taken by the other countries. Each country was also to notify the six other countries when it had completed its action.
The simultaneous-action provision of the treaty leaves open the possibility that
(A) the compliance date was subject to postponement, according to the terms of the treaty
(B) one of the countries might not be required to make any changes or take any steps in order to comply with the treaty, whereas all the other countries are so required
(C) each country might have a well-founded excuse, based on the provision, for its own lack of compliance
(D) the treaty specified that the signal for one of the countries to initiate action was notification by the other countries that they had completed action
(E) there was ambiguity with respect to the date after which all actions contemplated in the treaty are to be complete

摘要了一下，为什么选C

关键词：CONDITIONAL ON意思为：DEPENDING ON CONDITIONS。即每个行动依靠其他国家的同时行动。
问题应该在第一句上面：
Seven countries signed a treaty binding each of them to perform specified actions on a certain fixed date, with the actions of each conditional on simultaneous action taken by the other countries。 七个国家共同约定在某天采取具体的行动。条件是其它国家同时采取相应行动。
这样的话，如果A没行动的，B就有理由不用行动。但是B不行动也可以作为A不行动的理由。因为是simultaneous action. 这样这件事就说不清啦。

我的问题是，E为什么不对？

因为这些国家约定好同一天进行行动on a certain fixed date,我想不明白，为什么他们会推诿别的国家没有行动，所以他们也不行动。我倒觉得，每个国家都行动了，只不过因为没有计划何时结束，所以不知道第一个停止行动的国家是谁，于是结束的日期不清，所以我选E。谢谢大牛指教！

还是有点confused

如果这道题目不仅仅是fixed date,还有fixed time，具体到几点几分几秒，这些国家还能有借口么？

另外，E为什么不对呢？还是不知道。。。