求教大全359--it的指代

359

In 1990's ,there are more babies born by women over thirty years old than under it

A than under it

B  than were they under it

这里的it指的是什么？是thirty years old么？为什么it可以指代岁数呢？那they又指代什么呀？

想问一下，一般句子里，they 是首先指代主句的主语呢？还是先就近指代？还是有什么其他的规则？谢谢NNS指点

答案是B

In 1990's ,there are more babies born by women over thirty years old than (babies born by women) under it (=thrity years old)  

答案是A吧

答案是A，前人讨论过

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