[求助]有关现在完成时的进行时态问题

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.  D  A

(A) having, for example, been prescribed a drug at a dosage too low to be effective or having been（虽然现在完成时的现在进行时形式怎么看都觉得很诡异，第一个就被我排除了，但是好像结构还很平行）

(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 for it to be effective, or were（too low a drug dosage for it to be effective罗嗦）

(E) for example, when they have a drug prescription with a dosage too low to be effective, or been

prep语法笔记里说having done形式肯定错啊，为什么这道题选A呢？