Studies of ice-polished rocks

kvitkod wrote: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 what are now 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 is B. I choice E, since "WHEN" relates to time (in our case WHEN modifies AGE).
Please explain the reason for B?
What is the difference btw WHAT and THAT in B and E?

force5 wrote:Dear kvitkod i would really appreciate if you can mask the original answer and quote the source. It gets really difficult to solve once you know the answer.

However here i go..
IMO- A is the best

Agassiz proposed a theory in 1837 and the ice ages existed before this . hence we should use past perfect. ruling out B, C and E.

now between A and D. the only problem with D is current temperate areas. He should have used an adverb "currently" to convey the right meaning instead of "current"

pemdas wrote:@clock, is there 'currently' in choice A? "force suggests this word for D

pemdas wrote:in E 'that' comes after 'now' - it must come after 'areas' to be grammatically correct;
in A there is a gap in time sequence - past perfect 'had existed' and present simple 'are'
in C 'age' and 'when' cannot be used as 'age' is not specific time, moreover 'where there were areas now temperate' is not correct. It must be 'where there were areas which are temperate now'
in D 'when' is used with "age" and 'current temperate areas' must be corrected to 'currently temperate areas'

kvitkod wrote: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 what are now 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 is B. I choice E, since "WHEN" relates to time (in our case WHEN modifies AGE).
Please explain the reason for B?
What is the difference btw WHAT and THAT in B and E?