[单项选择]Passage 2 The top of the world is a wonderland. In winter, the temperature often falls to -30°F and the sun never rises. The ocean is surrounded by frozen ground. There are few people or trees, but to polar bears, the Arctic(北极)is home. (78) Polar bears have thick fur, big paws and other features that make them well prepared for life in their tough environment. In fact, they need the Arctic sea ice for survival. But climate change is causing larger and larger areas of summer sea ice to melt(融化). Experts say that if warming patterns continue, the Arctic could be free of summer sea ice by 2050. That may cause two-thirds of the world’s 20,000 polar bears to be gone by then too. Polar bears can’t survive for long on land. Seals are their main source of food. The only place where polar bears can hunt seals is on the ice. (79) Although these bears are strong swimmers, they are no match for lightning swift seals in the water. A polar bear has brilliantly clever strategies to overcom
A. Climate Change in the Arctic
B. How to Protect the Environment
C. The Arctic Ts Home to Polar Bears
D. Polar Bears in Danger

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