求NN解释，前后比较如何省略

酸辣年糕

       than前后比较，有的时候可以省略，有的时候不可以，真的很晕。。。求NN解释啊

l To develop more accurate population forecasts, demographers would have to know a great deal more than now about the social and economic determinants of fertility.

l Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than in any previous election.

第一句话不对，now应该改成they do now

第二句话对，可以省略

有疑问的是：

1.如果第一句话在前面加上in the future等时间词那么是不是只用now也可以，比如：

To develop more accurate population forecasts, demographers in the future would have to know a great deal more than now about the social and economic determinants of fertility.

因为比如这样的例子：The animosity between those who regulate and those who are regulated has never been more pronounced than in recent debates over environmentalism and pollution control.这句话就是对的，因为never和 in recent debates相对应

2.如果第二句话in去掉的话：

Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than any previous election.

那么是不是就不对了呢？

真的很混乱，求大神拍醒

咖啡印象

推荐楼主看看RON大神关于比较的讲解吧，没准儿能豁然开朗

http://www.manhattanprep.com/gmat/forums/post108547.html?hilit=omission&sid=690f50b602b417b61a4cef36a0d8d0b6#p108547

emmahiggins09

咖啡印象 发表于 2017-1-3 18:22
推荐楼主看看RON大神关于比较的讲解吧，没准儿能豁然开朗

http://www.manhattanprep.com/gmat/forums/post ...

必须赞，RON大神比较讲解，化腐朽为神奇，见一次赞一次

5Day

个人理解，不一定完全对，希望有帮助。

Parallelism或者对仗原则，than也可以在某种程度上看作是要求并列的。第一个句子比较的是know（or knowledge）而不是时间，要知道更多，而时间其实是用时态来表示了，would/do。楼主的改法我不太敢说是对不对，但是我可能会改为future demographers would have to know a great deal more than current ones，比较未来和现在demographers。

第二个句子，比较的的确是costs，但比较出的区别主要是在时间上，也就是in the presidential campaign of 1992和in any previous election。Parallelism的话，in最好不要省略。