prep07 语法2 T21 求助！

铭HAO

21. (25520-!-item-!-188;#058&002357)
Before scientists learned how to make a synthetic growth hormone, removing it painstakingly in small amounts from the pituitary glands of human cadavers.
(A) scientists learned how to make a synthetic growth hormone, removing it painstakingly
(B) scientists had learned about making a synthetic growth hormone, they had to remove it painstakingly
(C) scientists learned how to synthesize the growth hormone, it had to be painstakingly removed
(D) learning how to make a synthetic growth hormone, scientists had to remove it painstakingly
(E) learning how to synthesize the growth hormone, it had to be painstakingly removed by scientists


这道题我在C、D之间徘徊，最终因为主动优于被动选择了D。。。但是答案是C，笔记上说D选项的it指代a synthetic growth hormone不符合逻辑，可是我看不出C和D逻辑上的任何区别啊，还望大神指点！

铭HAO

大神。。。。。。。。。

dingdingtop

句子的逻辑意思错。意思变成了科学家在学习合成前，必须先从。。。小批量移走。it指代a synthetic growth hormone不符合逻辑，变成了任何一个、某一个synthetic growth hormone的意思。