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.
Option Elimination -
(A) than those that charge - "as...as" comparison marker at play. E.g., Deepika is as tall as her sister. "as ...than" is wrong.
(B) than are charging - same as A
(C) than to charge - same as A
(D) as charge - 3X as many institutions charge $X as charge $Y. If you are looking for where is "institutions after another "as"? Then, here, omission is at play. Here is a similar question if we would like to consolidate our learnings.
https://gmatclub.com/forum/patience-lov ... l#p3290813(E) as those charging - 3X as many institutions charge $X as institutions charging $Y - "institutions" after second "as" or no institutions - it doesn't matter as both are ok. But changing from the verb "charge" to verbal "charging" is not ok. ING word without helping verb is verbal and not a verb. Wrong.