Thanks for the clarification, Tim. I am sorry to disagree with you about the tense issue. I think the issue here is that the two clauses are linked by 'but' and when we link clauses by 'and' , 'but' we do not need past perfect , we do with simple past (Strategy guide says). Also, I found in the guide that past perfect is used when earlier action has a bearing on the later action.

Please comment.

Tim is making a great point about what "had been" really means. Consider this sentence:

"The house had been green before it was repainted blue."

This shows how "had been" works; it indicates that something or someone used to have some quality or status but now does not. Ask yourself whether that is really an accurate way to describe the lava in this sentence; was it an underground remnant only until the scientists came along? That meaning doesn't make sense.

To be clear, we should use simple tenses as much as possible; the GMAT prefers the use of the simple tense to the use of the complex tense. We should use the complex tense past perfect if we have two past events and we are going to distinguish which one happened earlier. Do not use past perfect if simple past will do just as well, and that is the case in this problem. About the parallelism issue, definitely check out the problem Tim referenced, #42 in the Official Guide, then let us know if you have further questions. Thanks!

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Jamie Nelson
ManhattanGMAT Instructor

thanks for the clarification.

:-)

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Jamie Nelson
ManhattanGMAT Instructor

this is a really great point i've never seen elsewhere.

so comma-ing rules are actually backwards when the -ing is having? because normally it is the -ing is a direct result of the main clause, not the other way around.

My examples:

i bought a cat, satisfying my need for a pet. normal comma+ing, where -ing is a direct consequence

i bought a cat, having satisfied my need for a pet. -wrong I think?

i bought a cat, having heard of a two-for-one sale - the main clause is the consequence of the having? this seems to make sense

having heard of a two-for-one sale, i bought a cat - this appears to be the same as the previous to me...

GMAT prep example,
Some patients ... may simply have received inadequate treatment, having been prescribed a drug as a dosage too low to be effective or having been taken off a drug too soon. <--correct

one of the staff said that in the GMAT prep example, having is "comma+ing" explains the manner in which the main clause occurred. That makes sense, but it kind of contradicts what i quoted from you.

sounds like you have the right idea. let us know if you need any further help on this topic..

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Tim Sanders
Manhattan GMAT Instructor