GWD-24-Q 20

GWD-24-Q 20:

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

正确答案为：E

为什么不选D？

those = institutions,

without those, it could be the comparation between independent institutions and charge