All和not连用，应当怎样理解？

tress

在语法书中not和all一起连用时，不表示完全否定，仅表示部分否定。如：All his children are not at school. 他的有些小孩在上学（有些小孩没在上学）。但是应当怎么理解如下这道题呢？请牛人指点。

Although all the proceedings of the Communist party conference held in Moscow were not carried live, Soviet audiences have seen a great deal of coverage.
a. all the proceedings of the Communist party conference held in Moscow were not carried live
b. all the Communist party conference's Moscow proceddings were not carried live
c. alll the Communist party conference Moscow proceedings have not been carried alive
d. not all the Communist party conderence Moscow proceedings have been carried alive
e. not all the proceedings of the Communist party conference held in Moscow were carried live

正确答案是e
解释中说在这里not all表示“并非所有”，但是为什么a的表达方式不可以？按照部分否定的原则，a不是也可以达到并非所有的意思吗？麻烦大家给些指点。

aeoluseros

嗯，对于部分否定GMAT好像只认not all.
关于all...not...还是有歧义的存在，所以它不喜欢。

Christine2099

同问，正好也做到这道题了。
虽然选了E，对的。但就是对A抱有幻想。
我们从小到大学的英语不一直告诉我们not all是部分否定吗，不管怎么放。
难道GMAT语法在这点上有明确规定不能all...not...表示部分否定？

请高人指教~