摸考遇到的语法题

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 or having been

B. having, for example, a drug prescrition that was ineffective because the dosage was too low ,or  being

C. as, for example,  having too low of a dosage  prescribed adrug for it to be effective, or being

D. when they have,  for example, been prescribed too low a drug  dosage to be effective, or were.

E. for example, when they have a drug  prescribed with a dosage too low to be effective ,or been