支持A.
因为A中就只有一处不妥:which的指代问题.
而B有两处不妥:
① they are mountain dwellers中的they指代不清,可以是the Rocky Mountains或elk
②The fact that elk now live almost solely in the Rocky Mountains would make it seem that they are mountain
dwellers, but
they once ranged over virtually all of the continental United States except for a small strip in the extreme Southwest. 句中是红字部分与兰字部分对比,从结构上看这两部分可以都是seem的从句,此时一个事实说明了两个截然相反的事实.这个问题在A中就没有,因为Elk now live almost solely in the Rocky Mountains, which would make it seem that elk are mountain dwellers, while they once ranged over virtually all of the continental United States except for a small strip in the extreme Southwest. 句中红字部分与兰字部分对比,which...是红字部分的定语从句,结构很清楚.