一.语法填空（每题2分，共20分）
Polar bears are suffering in a 1. _______ (warm) world than ever before.
Polar bears live in environments too cold for most animals. 2 _______much of the year, they live and hunt on the frozen Arctic sea ice. Nature has prepared them for the cold 3._______(condition). But nothing has prepared the bears for the danger that 4.________ (threat) the only home they know.
