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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 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在科学家们懂得如何合成生长荷尔蒙之前，它不得不被辛苦得从人体死尸的垂体腺中一点一点地提取。 D. learning how to make a synthetic growth hormone, scientists had to remove it painstakingly在懂得如何合成生长荷尔蒙之前，科学家们不得不辛苦得从人体死尸的垂体腺中一点一点地提取它。 E. Learning how to synthesize the growth hormone, it have to be painstakingly removed by scientists
不是NN,大概看个意思吧
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发表于 2006-12-30 16:44:00
