[求助]og119,请nn指点

119. 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（B）

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

Choice B, the best answer, uses clear and concise phrasing to state that it is the effects of drug and alcohol abuse that already cost business the sum mentioned. In A, to business is awkwardly and confusingly inserted between cost and the prepositional phrase that modifies it, and are already a cost to business is wordy and awkward compared to cost business. In C, already with business costs of... is awkward and unclear, failing to specify that those prior effects generate the cost. Choices D and E produce faulty constructions with the phrase significant in compounding, which cannot grammatically modify the verb form is growing.

我的问题：1Choices D and E produce faulty constructions with the phrase significant in compounding, which cannot grammatically modify the verb form is growing.是什么意思？ 特别请nn解释一下蓝体部分。难道是指significant in compounding修饰is growing?可是compounding有做什么成份？

2 compounding的逻辑主语是什么？

3 否定e，是由于significant in 改变了significantly的意义，但是og的解释认为significant in不 modify 宾语is growing,可是如og所说，那么可以解释为（is）significant in。

请大家帮忙！实在想了很久，看了所有的有关帖子，但是还是没有解决。

实在诚心感谢。问题很愚钝，但是希望nn赐教。