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.
(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
OG解釋是說
1. in which or when can be used interchangeably in this sentence
2. The verb form here should be the simple past tense existed rather than the past perfect had existed.
我的問題是:
1.when不會比較好嗎? 這兩者是都可以用
還是有什麼情形in which 不能代替when
2.為什麼用過去簡單式? 我第一選直覺就把簡單式劃掉選過去完成式了
句子裡前面的led不是已經是簡單式了?
exist有沒有過去完成式的用法呢??
謝謝!!