885SC-9-26疑惑

26.   Executives and federal officials say that the use of crack and cocaine is growing rapidly among workers, significantly compounding the effects of drug and alcohol abuse, which already are a cost to business of more than $100 billion a year.

(A) significantly compounding the effects of drug and alcohol abuse, which already are a cost to business of

(B) significantly compounding the effects of drug and alcohol abuse, which already cost business

(C) significantly compounding the effects of drug and alcohol abuse, already with business costs of

(D) significant in compounding the effects of drug and alcohol abuse, and already costing business

(E) significant in compounding the effects of drug and alcohol abuse, and already costs business

答案是B，请问这是什么结构呀，为什么E不合适那？

多谢多谢，^_^