Polar bears are suffering in a much ____ (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 ____ （prepare）them for the cold conditions. But nothing has prepared the bears for the danger ____ threatens the only home they know.

    The polar bears' world is melting. Studies show that the amount of the polar ice ____（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 ____ the sea ice for their survival. “The sea ice is more ____ just this platform that the bears walk over,” says Andrew Derocher, ____ scientist who studies North American polar bear populations. “____ 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 ____ (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 ____(active) hunting.