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题库 / Prep2007E2-SC-21
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
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1. if the subject of a verb is unknown or irrelevant, use the passive voice.
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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