请教一道关于平行比较的题目。

MsL

GWD-12-Q30:
According to public health officials, in 1998 Massachusetts became the first state in which more babies were born to women over the age of thirty （than） under it.

A.        than
B.        than born
C.        than they were
D.        than there had been
E.        than had been born

正确答案为A

请问是it指代了 babies were born to women ？ 好像it不可以指代句子。
还是more...than...结构如果主语相同可以省略？
应该怎样解释这道题呢？

rain009

it指代了 the age of thirty

MsL

more...than...结构不是要平行吗？
这样就变成了more babies... than under the age of 30.

MsL

more和than比较的对象就不一样，more后面是baby, than后面是年龄。

qiongle

这道题是省略吧 more babies were born to women over the age of thirty than  【babies were born to women】  under it （the age of thirty）.【】里面是省略的部分（）里面是it的指代对象。