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

OA some posts below

Source - GMATPrep by Pearson VUE

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 (incomplete sentence is what i'll call it. out)
B scientists had learned about making a synthetic growth hormone, they had to remove it painstakingly (had learned is wrong use of tense)
C scientists learned how to synthesize the growth hormone, it had to be painstakingly removed (what is 'it', or what does it refer to? it should be 'they' following/meaning scientists)
D learning how to make a synthetic growth hormone, scientists had to remove it painstakingly (best choice)
E learning how to synthesize the growth hormone, it had to be painstakingly removed by scientists (same as C)

(D) for me

The only choice that makes sense grammatically is C and D.

From my point of view, D is grammatically correct but the meaning is totally wrong....

Lets break down D,

Before learning how to make a synthetic growth hormone, scientists had to remove it painstakingly in small amounts from the pituitary glands of human cadavers.

Now look at the independent clause, it has "IT", a pronoun that must refer back to a noun it represents. In this case it is "a synthetic growth hormone".

synthetic means a product that is made from artificial substances. So the sentence becomes

Before learning how to make a synthetic growth hormone, scientists had to remove (a synthetic growth hormone), aka it, painstakingly in small amounts from the pituitary glands of human cadavers.

So D says, a synthetic growth hormone was already existing in the pituitary glands, which can not be the case...

Lets see what C says,

Before scientists learned how to synthesize the growth hormone, it (refers clearly to the growth hormone) had to be painstakingly removed in small amounts from the pituitary glands of human cadavers.

C makes perfect sense... C says, before scientists learned to synthesize ( make it artifically) the growth harmone, it had to be removed.

What do you guys think, AM I LOSING MY MIND.....

Thanks Paul as usual for your explaination. But I still believe that D will make more sense if the word synthetic is changed to adverb.

Good question and the explanation is spot-on. Agree with C for the same reason: one cannot extract a synthetic hormone

I picked C. Its the only one (apart from B) which makes sense. I've read that the GMAT SCs now test quite a bit on the actual 'meaning' of the sentence. B is out because it uses perfect past in 2 places with no real need.

The sentence is clearly trying to state that before a synthetic version of the GH could be made, scientists had no option but to use the real thing.

Right. (C) is the correct one.

(D) seems to indicate that it was the "scientists" who used to sit and painstakingly remove the hormone in earlier times....which is unlikely.
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