疑惑了。。请帮帮忙下，新prep1-202

Providing initial evidence that airport are a larger source of pollution than they were once believed to be, environmentalists in Chicago report that the total amount of pollutant emitted annually by vehicles at O’Hare International Airport is twice as much as that which is being emitted annually by all motor vehicles in the Chicago metropolitan area.

1. as much as that which is being emitted annually by all

2. as much annually as is emitted by the

3. as much compared to what is annually emitted by all

4. that emitted annually by all

5. that emitted annually compared to the

选的时候只想到twice+the+n，就选了D

可是发现这里that是作代词吗？不是this和that一般不能单独指代的吗？

请指教下啊！

哦。。。。是这样啊，我以前听xdf老师说that，this是不可以用来单独指代的，后面必须加名词。。。

那个应该是说that，this之类的词不能指代前面的整个句子，而不是单独的词。

这里that指代the amount。我选D。正确答案是啥？

哦。。是这样的啊。。。正确答案就是D