求助Prep1 - 154

chuRiver

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













答案A。答案中说要特别注意，相同的词在并列句中起不同作用，比如have做助动词和实义动词时，就不可以省略。看不出A中两个having的作用哪里不一样了？