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


The answer is A.

I picked E - can someone explain why is E incorrect -

It looks like there are some typos in the original:
who do not respond TO therapies FOR depression?

In any case, the verb tenses are inconsistent in E:

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

To shorten it: "...when they have X and been Y". It doesn't work. It should be something like "when they have been X and have been Y" or "having been X or having been Y" as in A.

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

I guess BD are incorrect because
B-having a drug prescription is not parellel with being taken off
D-they have been is not parellel with were taken off


but I am not sure. Is there any other mistakes in these two choices?

thanks.

C would be incorrect because of Parallelism as well. Note that "as" creates a comparison, which is a special case of P-ism. Here the "as" connects "having too low a dosage" with "treatment." The same is the case with E, in a way, as the example give is not an example of a "treatment."