请教老prep2第21题

甜蜜小乌龟

Before scientists learned how to make a synthetic growth hormone, removing it painstakingly in small amounts from the pituitary glands of human cadavers.C scientists learned how to synthesize the growth hormone, it had to be painstakingly removed.
D learning how to make a synthetic growth hormone, scientist had to remove it painstakingly


正确答案应该选c 我选的是D 语法笔记解释说D错在it 指代the growth hormone不合逻辑 我想问为什么不合逻辑 我当时选D 的原因是觉得D的表达更简洁 it指代也能说清不会造成歧义啊 这是为什么呢？

甜蜜小乌龟

自己顶一下 等待牛牛们来指教