The surest way of stopping the manufacture of methamphetamine is

Dear nitiny,

I'm happy to respond. I'm sorry to say, this SC practice question is not of the highest quality.

We don't need to have an infinitive after the verb to match the infinitive before the verb. Choice (C) is really not much better than (A) & (B); those latter two are certainly not "wrong enough" by GMAT SC standards. Choice (D) has some awkward wording, and choice (E), with a different verb tense, appears to change the meaning. This raises the question why the prompt or OA doesn't use a conditional tense:
The surest way to stop the manufacture of methamphetamine would be to require a prescription for its essential ingredient, pseudoephedrine.
That would match the state of affairs in the real world, to my understanding.

This SC practice question has a lot of words, including big words, and a lot of underlined real estate, with not much actually going on. Notice that more than necessarily is underlined: the first words and the last word do not need to be included in the underlining: that's a very basic mistake on the part of the question writer. As a question writer, I would give this question an F.

Here's a much higher quality SC practice question, with less underlined but more going on:
Although more expensive

Does all this make sense?
Mike

The surest way of stopping the manufacture of methamphetamine is the requirement for a prescription for its essential ingredient, pseudoephedrine.
A. The surest way of stopping the manufacture of methamphetamine is the requirement for a prescription for its essential ingredient, pseudoephedrine. - Not parallel.
B. The surest way to stop the manufacturing of methamphetamine is requiring a prescription for its essential ingredient, it being pseudoephedrine. - Not parallel.
C. The surest way to stop the manufacture of methamphetamine is to require a prescription for its essential ingredient, pseudoephedrine. - CORRECT
D. The surest way of stopping the manufacture of methamphetamine is requiring of a prescription for their essential ingredient, pseudoephedrine. - Not parallel, pronoun problem.
E. The surest way to stop the manufacture of methamphetamine has been to require a prescription regarding its essential ingredient, which is pseudoephedrine. - Total mess.