The reasons for the pollution of Ganges were either because it is an easy target for effluents with several of its tributaries like Yamuna, Gomati etc flowing through industrial belts or for the simple reason that it had a massive catchment area in the thickly populated North India.

A. that it had a massive catchment area in the thickly populated North India
B. that its catchment area was massive in the thickly populated North India
C. that it caught massive areas in the thickly populated North India
D. of its massive catchment area in the thickly populated North India
E. of its thick catchment area in the massively populated North India
[spoiler]OA.A
Why use had here ?? is there any action happening after "massive catchment". Isn't the question same to the one given below. Both have only one action that actually occurred in past.

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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