Before scientists learned how to make a synthetic growth hormone, removing it painstakingly in small amounts from the pituitary glands of human cadavers.
scientists learned how to make a synthetic growth hormone, removing it painstakingly
scientists had learned about making a synthetic growth hormone, they had to remove it painstakingly
scientists learned how to synthesize the growth hormone, it had to be painstakingly removed
learning how to make a synthetic growth hormone, scientists had to remove it painstakingly
learning how to synthesize the growth hormone, it had to be painstakingly removed by scientists
2.In the problem at hand, the original sentence, along with answer choices B and D, indicate that scientists removed "a synthetic growth hormone" from cadavers. This is nonsensical, as something synthetic, by definition, does not come from a natural source. Thus, A, B, and D can be eliminated based on their lack of clarity.
排除掉ABD,CE里面比最优,E: "before learning"修饰的是scientists,和主句主语矛盾。
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