289、 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（B）

请问：B中的which指代什么？我以为是指代前面的整句话而产生的影响，所以做题时立刻开始找-ing，结果没有。

which 是修饰effects 的.

另外强烈推荐楼主看一下OG, 里面的解释相当清楚.

谢谢.