有关than 的用法！！

bibby00888

30．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.

什么时候than 后面能省略啊！！！求达人！！

CD用户726223

状语之间的比较啊，比较中句子成分、形式相同的部分(如此题的to women)往往省略