英语爱好者进：英语单项的解读

as is reported in the newspaper, talks between the two counties , are making progress

开头的为是么不能用that ？这里是状语，那that 不是可以充当主语的吗？在什么时候她可以充当句首的状语呢？还有what 呢？

我理解的是这样的：

as指代整个主句的内容，就是 talks between the two counties , are making progress ，定语从句里可以指代整个句子的只有as和which，that不可以。而且如果置于句首的话只能是as。而且as还比which多一层意思就是“正如……那样”。that当然可以充当主语，但是不能指代整个句子，所以这里不可以。而what就更不可以了。what在名词性从句里身兼两职，=the+名词+that。非用what的话句子只能这样做What is reported in the newspaper is that talks between the two counties are making progress。这就是主语从句+表语从句了。

as is reported in the newspaper是状语， talks between the two counties 充当主语，are making progress 是谓语和宾语，as 在状语中作主语，假如换成其他连词，语法上是错误

as is reported in the newspaper, talks between the two counties , are making progress

as引起整个句子~或者用as what is reported in。。。这时as做连词~what才引起主语从句~

as引导的非限制性定语,没有that这种用法

①as引导的非限制性定语从句可放于主句前、主句中、主句后，而which引导的非限制性定语从句一般放于主句后或句中。as放在句首的情况常用的句式 有as we all know,as is mentioned above,而which我们则看不到这样用于句首的情况。 ②as常与从句中的know，see， hear，expect等动词连用，也常用于as often happens，as is often the case（常有的事）等句子中；而which一般不用于以上情况。 ③as有“正如”的含义，which没有此含义。如： As is well known，Shanghai is a big city． Some of the roads were flooded， which made our journey more difficult．