题目内容：

Polar bears live in environments too cold for most1.(animal).For much of the year,they live and hunt on the 2.(freeze) Arctic sea ice.Nature has prepared them for the cold conditions.But nothing has prepared the bears for the danger3.threatens the only home they know.

The polar bears' world is melting.Studies show that the polar ice4.(reduce) by 9.8% every 10 years since l978.Now about 20,000 to 25,000 polar bears live in the Arctic.Polar bears depend on the sea ice for their5. (survive)."The sea ice is more6.just this platform that the bears walk over,"says Andrew Derocher,a scientist who studies North American polar bear populations."Without7.,they can't exist."

Some melting and refreezing of the polar ice is8.(nature).But in a warmer world,these cycles speed up,and bears have9.(little) time to hunt.Normally,they have three months in the spring when they gain more weight.The extra fat is used10.(late),when the bears are not actively hunting.