请教一道prep语法题

花花臭臭 · 发表于 2012-11-23 11:23:20

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
选C，我选的D. 觉得C/D没有什么区别。请问到底是咋回事呀？

yiqing2012 · 发表于 2012-11-23 21:13:31

http://www.manhattangmat.com/forums/before-scientists-learned-how-to-make-a-synthetic-growth-t637.html
ps

Z~ 下次问问题之前可以先查一下老帖子哦~~ 这道题有很多人都问过了呢~~O(∩_∩)O~

请教一道prep语法题

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