tense

[GMAT Kolaveri]

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 now currently temperate areas.

(A) in which great ice sheets had existed 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

OA: B

But i prefer D. I think had is necessary. but B does not "had"

[vk_vinayak]

It's a contest between A and B.

A is clearly wrong because between now and currently, only one is needed.

Also, had is not necessary here. Had is used only when we want to showcase the sequence of events. In the current sentence, the sequence is very clear, hence no need of 'had'.

[GmatKiss]

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 now currently temperate areas.

(A) in which great ice sheets had existed 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

[Bill@VeritasPrep]

Also, had is not necessary here. Had is used only when we want to showcase the sequence of events. In the current sentence, the sequence is very clear, hence no need of 'had'.

Exactly. If the events are unrelated, we do not need past perfect.