Prep2007 1-35

我吃果冻

35. 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

正确答案C

-------------------PREP 解释-------------------

(A) promotes…, but not…interfering…结构不平行

(B)  错误同A选项；

(C)  正确, a substance that…独立主格结构作为thromboxane的同位语对thromboxane进行解释说明; but does跳过同位语和suffices并列共同作为a low dose of aspirin的谓语动词

(D) but does…更像是跟is a substance…并列,从而作为了thromboxane的谓语动词,改变了原句的意思

(E) but not a serious语法上只能跟is a substance并列(因为前面有which is a substance that…所以but not a serious…可以视为but is not a serious…的省略结构,但是却不能做为…usually suffices的省略结构),共同修饰thromboxane,改变了原句的意思

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有几个问题请教大家：

1.这个句子里，a substance that...不是一个单纯的同位语+限制性定语从句吗，为什么说是独立主格结构？

2. does not seriously interfere为什么是跳过同位语，和suffices并列，而不是和promotes blood clotting并列？

kyle7

为什么D中的but does not 就不可以跳过前面的which呢～求解答～

我吃果冻

谢谢啦。你说的第2点，我又重新研究了一下，如果是和promotes并列虽然语法上没有错误，但是会产生这样的情况：
In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane,(主句结束)a substance that promotes blood clotting, but does not seriously interfere with the production of prostacyclin, which prevents clotting.(后面就全是thromboxane同位语的成分了，显然句子结构不合理)
同时，我觉得如果真的是和promotes并列的话，but前的comma应该去掉，这样表达更加准确。
多谢解惑！

gmatbiguo

（1）a substance that...的确是一个同位语，不是独立主格
（2）连接词but是连接两个主句的。而且，从这道题的平行对称结构上看，也是和和suffices并列，构成一个和完美的平行对称结构。
In laboratory rats, a low dose of aspirin usually suffices ..., a substance that ..., but not seriously ..., which prevents ...