题目选项分析

According to scientists at the University of Alaska, while the surface temperature of the globe has risen over the last century by about one degree Fahrenheit, the surface temperature in Alaska, Siberia, and northwestern Canada has increased over the last thirty years by about five degrees.

According to scientists at the University of Alaska, while the surface temperature of the globe has risen over the last century by about one degree Fahrenheit, it has increased in Alaska, Siberia, and northwestern Canada over the previous thirty years by about five degrees.