8. 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. scientist 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 have to be painstakingly removed by scientists
正确答案是：C
为什么D不对呢？
1请帮忙解释；
2告诉我从哪入手做的，谢谢……
两者还是不同得，
C中 it 指代 the growth hormone更合逻辑，而D中it指代a synthetic growth hormone；两者是不同得。
同时， how to synthesize 和how to make a synthetic growth hormone中，前者更effective一些。
楼上说的没错
关键就是细比较C与D，就会发现，两个选项中的it指代不同
C中指的是the growth hormone，D中指的是a synthetic growth hormone
那么科学家要制造哪一个呢？当然是前者了
所以选C
P.S.请楼主在这个版里下一个《PREP破解版语法注释分析》
PREP中的问题全在这里面：）
很方便的！
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