Before scientists learned how to make a synthetic growth hormone, removing it painstakingly in small amounts from the pituitary glands of human cadavers.
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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 分析A选项
B scientists had learned about making a synthetic growth hormone, they had to remove it painstakingly 分析B选项
C scientists learned how to synthesize the growth hormone, it had to be painstakingly removed 分析C选项
D learning how to make a synthetic growth hormone, scientists had to remove it painstakingly 分析D选项
E learning how to synthesize the growth hormone, it had to be painstakingly removed by scientists 分析E选项