GMAT Sentence Correction (SC) | Re: GMATPREP ChallengeQ -Some patients who do not respond to the

Here is my explanation with some additional concepts:

A.having, for example, been prescribed a drug at a dosage too low to be effective or having been

Statements beginning with 'having' are tricky and you have to be extra careful using them. Generally these statements refer to an event that has happened prior to another event mentioned in the sentence. Now lets move on to the first answer choice: the 2 events 'drug prescription' and 'patients being taken off a drug too soon' happened before
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