题目内容：

Polar bears are suffering in a much 1. (warm) world.

Polar bears live in environments too cold for most animals. During much of the year, they live and hunt on the frozen Arctic sea ice. Nature has 2. （prepare）them for the cold conditions. But nothing has prepared the bears for the danger 3. threatens the only home they know.

The polar bears’ world is melting. Studies show that the amount of the polar ice 4.（have）decreased by 9.8% every 10 years since 1978. Now about 20,000 to 25,000 polar bears live in the Arctic. Polar bears rely 5.the sea ice for their survival. “The sea ice is more 6. just this platform that the bears walk over,” says Andrew Derocher, 7. scientist who studies North American polar bear populations. “8. it, they can’t exist.”

Some melting and refreezing of the polar ice is natural. But in a warmer world, these cycles speed up, and bears have less time 9. (hunt). Normally, they have three months in the spring when they gain more weight. The extra fat is used later, when the bears are not 10.

(active) hunting.