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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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选项A 句子无主谓
选项B Before后跟过去完成时态错误，因为learn应该在主句动作remove时间之后;it指代synthetic growth hormone不符合逻辑。
选项C 正确 Before scientists learned how to synthesize the growth hormone,it had to be painstakingly removed in small amounts from the pituitary glands of human cadavers.
选项D it指代synthetic growth hormone不符合逻辑。
选项E learning 逻辑上不修饰IT
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