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
Why C?
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