单选题 .  ①Although some skeptics points to Arctic places such as the high latitudes of Greenland, where temperatures seem to have fallen, a recent scientific report concludes that in recent decades average temperatures have increased faster in the Arctic than elsewhere. ②Scientists have long suspected that several factors lead to greater temperature swings at Earth's polar regions than elsewhere. ③First, most of the Arctic is covered in snow and ice, which are highly reflective; if snow and ice melt, the exposed soil, which absorbs heat, serves to accelerate warming. ④Second, the polar atmosphere is thin, so little energy is required to warm it. ⑤Third, less solar energy is lost in evaporation at the frigid poles than in the tropics.34.  The passage mentions which of the following as factors that might lead to large temperature swings in Earth's polar regions? ______