新PP test2 Q39

[coulomb]

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

答案給C我選D
A後半句沒動詞 不用看
B用過去完成式 沒必要
CE用被動感覺怪怪的 所以當初選D
請教一下CDE要怎麼看呢？謝謝

[sisco]

synthesize 優於 make a synthesitic 動辭優於形容詞 且簡潔 D E 刪掉

painstakingly 修飾removed D 修飾it 刪掉