Brutal SC 1

[ranjeet_1975]

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

A -- having, for example been prescribed a drug as 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 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
E -- for example, when they have a drug prescription with a dosage too low to be effective, or been

OA is A, Please explain. I can't understand the use of having - please help.

[ranjeet_1975]

Please KillGmat help me on the subject

[raunekk]

uses " having been" as present perfect continous tense (rare usage)for the prescribed dosage still having effect..as the sentence is in present tense.Also "having been" is perfectly used in parallel!!