请教prep上的一个语法题

154.
            (答案是A我选了C，请NN指教，非常感谢)

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 prescription that was ineffective because the dosage was too low, or being

(C) as, for example, having too low of a dosage of a prescribed drug 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 prescription with a dosage too low to be effective, or been

这个就一个考点吧，or前后的平行并列，只有A是 having been...or having been.

分词在句尾表伴随。