请教prep一道题目，语法笔记里没有

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In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane, which is a substance that promotes blood clotting, but not seriously interfering with the production of prostacyclin, which prevents clotting.

(A) which is a substance that promotes blood clotting, but not seriously interfering

(B) a substance that promotes blood clotting, but not seriously interfering

(C) a substance that promotes blood clotting, but does not seriously interfere

(D) which is a substance to promote blood clotting, but does not seriously interfere

(E) which is a substance that promotes blood clotting, but not a serious interference

答案C，想问D为啥不对？？

1。WHICH IS是可以省略的，不影响句子的意思；在本题中，同位语比定从简洁，符合简洁的原则。

其实做OG多了，就知道which is/that is结构是wordy的结构。

2。对于substance，理解题意是解释说明substance的作用，而不是用to promote来表示目的，不是这个substance是用来做甚么的。

欢迎其他意见。