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) 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 (C) 正确,it指代the growth hormone(明确it的指代对象,是做对本题的关键)。 (D) it指代synthetic growth hormone不符合逻辑。 为什么D错? 不理解,it可以指代learning how to make a synthetic growth hormone分词短语?? |