白勇语法第8章语法第34练习题，高手帮助

34.His studies of ics-polished rocks in his Alpine hone-land,far outside the range of present-day glaciers,let Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in now currently temperate areas

a.

b.in which great ice sheets existed in what are now temperate areas

选项b中里放了个what,应该有误吧,

in which great ice sheets existed in what are now temperate areas

当需要使用that which时用what代替。