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

Some patients who do not respond to therapies for depression may simply have received inadequate treatment,having, for example, been prescribed a drug at a dosage too low to be effective or having been taken off a drug too soon.

A.having, for example,been prescribed a drug at a dosage too low to be effective orhaving been
Correct. Parallelism: modifier // modifier.

B. having, for example, a drug prescription that was ineffective because the dosage was too low, orbeing
Wrong. Not parallel.