求助GMAT一道语法题

题目

求助GMAT一道语法题
According to a 1996 survey by the National Association of College and University Business Officers,more than three times as many independent institutions of higher education charge tuition and fees of under $8,000 a year than those that charge over $16,000.
A.than those that charge
B.than are charging
C.than to charge
D.as charge
E.as those charging
我选的是D,而答案是E,应该是考察平行结构,但是E是如何平行的忘高人指点
后面的as those charging很明显不是句子

答案

as.as的平行结构
E:as+句子.as+句子构成的形式平行.
D选项：as charge,charge缺乏主语,无法和前面的many independent institutions of higher education CHARGE tuition and fees...平行.