阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。

Polar bears live in such environment that is too cold for most animals. For much of the year, they live and hunt on the 【小题1】 (freeze) Arctic sea ice. Nature has prepared them for the cold conditions but nothing has prepared them for the danger 【小题2】 threatens their only home.

Polar bears’ world is melting. Polar bears 【小题3】 (suffer) in a warmer world are in danger. Studies show that the polar ice 【小题4】 (reduce) by 9.8% every ten years since 1978. At present, 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 the platform that the bears walk 【小题6】.” says Andrew Derocker, who studies North American polar bear population. “Without it, they can’t exist.”

Some melting and refreezing of the polar ice is nature. But in 【小题7】 warmer world, these cycles speed up, and bears have 【小题8】 (little) to hunt. 【小题9】 (normal), they have three months in the spring when they gain more weight and the extra fat 【小题10】 (use)   later, when the bears are not actively hunting. Therefore, it’s urgent to protect the environment and maintain the ecological balance.