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.
in which great ice sheets had existed in now currently temperate areas
in which great ice sheets existed in what are now temperate areas
when great ice sheets existed where there were areas now temperate
when great ice sheets had existed in current temperate areas
when great ice sheets existed in areas now that are temperate
E选项中的now 是修饰的existed,这是不对的,应该放在that are temperate里面
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