| 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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| (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) scientists learned how to synthesize the growth hormone, it had to be painstakingly removed |
| (D) learning how to make a synthetic growth hormone, scientists had to remove it painstakingly |
| (E) learning how to synthesize the growth hormone, it had to be painstakingly removed by scientists |
