According to a 1996 survey by the National Association of College an 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
What could be the answer for this. The OA says D. Can someone please shed some light?