Please post the complete question. I think this is from OG.

One can only answer you queries with reference to complete sentence.

Thanks

Hey Derek,

Good question - and like the other poster said it's a lot easier to help with this particular GMAT question if you can post the whole thing.

As far as which/when/where:

"When" must describe time.
"Where" must describe location.
"Which" can describe a variety of nouns.

So if choice B led with: Scientists continue to conduct extensive research regarding the Paleolithic Period, in which...

"Which" modifies "period", and that's okay. "When" would still work, too, because the Paleolithic Period is a time frame.


Say it led with: Glaciers had an incredible impact on the Great Lakes region, ___________________

You couldn't use "when" (because it doesn't describe time), but "in which" would still work, with "which" taking the place of "region".


It's definitely not true that "in which" is "always" wrong. Honestly, I can't think of any phrases that you could ever say are "always" wrong - in that case, why would they exist?

My strategy on questions like this - use the when/where/who (must describe a person) pronouns to get rid of illogical replacement ("when" modifying a place or "who" modifying a time...that kind of thing) and then see what that lets you eliminate. "In which" is going to be right in some cases, but you really don't need to be an expert on all of those...you can typically use the more-egregious errors to get rid of enough sentences that you can use context to get you through the rest.

Thank for the answer! Here is the whole question I missed above.

His studies of ice-polished rocks in his Alpine homeland, far outside the range of present-day glaciers, led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in what are now temperate areas

(A) in which great ice sheets had existed in in now currently temperate areas
(B) in which great ice sheets existed in what are now temperate areas
(C) when great ice sheets existed where there were areas now temperate
(D) when great ice sheets had existed in current temperate areas
(E) when great ice sheets existed in areas now that are temperate