没找到GWD-8-Q18语法题的讨论，请教各位

ceecn2000

请教：

According to a recent study of consumer spending onprescription medications, increases in the sales of the 50 drugs that wereadvertised most heavily accounts for almost half of the $20.8 billionincrease in drug spending last year, the remainder of which came from salesof the 9,850 prescription medicines that companies did not advertise or advertisedvery little.

A.    heavily accounts for almost half of the $20.8 billion increase in drugspending last year, the remainder of which came

B.    heavily were what accounted for almost half of the $20.8 billion increasein drug spending last year; the remainder of the increase coming

C.    heavily accounted for almost half of the $20.8 billion increase in drugspending last year, the remainder of the increase coming

D.    heavily, accounting for almost half of the $20.8 billion increase in drugspending last year, while the remainder of the increase came

E.     heavily, which accounted for almost half of the $20.8 billion increase indrug spending last year, with the remainder of it coming

正确答案C中为什么用coming？我知道如果用came，那么逗号要改分号，或者加and，但是coming是个什么用法？
谢谢～