请教GWD-10-10

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

我选的是E呀。我觉得比较对象是institutions,所以不解怎么可以没有those,

答案不是E吗？