Polar bears are suffering in a【小题1】(warm) world than ever before.Polar bears live in environments too cold for most animals. For much of the year,【小题2】live and hunt on the frozen Arctic sea ice. Nature has prepared them for the cold conditions. But nothing has prepared the bears for the danger threatening the only home【小题3】they know.The polar bears’ world is melting. Studies show that the polar ice【小题4】(reduce) by 9.8% every 10 years since 1978. Now about 20,000 to 25,000 polar bears live in the Arctic. Polar bears depend on the sea ice for their【小题5】(survive). “The sea ice is more than just this platform that the bears walk over.” says Andrew Derocher,【小题6】scientist who studies North American polar bear populations. “【小题7】it, they can’t exist.”Some melting and refreezing of the polar ice is natural. 【小题8】in a warmer world, these cycles speed up, and bears have less time【小题9】(hunt). Normally, they have three months in the spring when they gain more weight. The extra fat is used later, 【小题10】the bears are not actively hunting.