单选题 The top of the world is a wonderland. In winter, the temperature often falls to -30℉ 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.
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 word"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. 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 overcome this disadvantage. In winter the bear waits motionless beside a seal"s breathing hole, which is a narrow tunnel through the ice. Often many hours pass before the seal comes up for air and the bear kills it with a powerful blow of its paw. In summer, the polar bears that live on land eat very little and wait for the sea ice to return.
With the sea ice forming later in the year and melting earlier, polar bears do not have enough opportunity to hunt and eat. Less sea ice makes it harder for the bears to catch the seals. The bears must swim longer distances between ice packs (大片浮冰), and they can"t always make it. The ice is also getting thinner. These conditions can cause polar-bear cubs to become separated from their mothers, who provide them with food.
Steven Amstrup is the chief scientist of Polar Bear International. The group aims to save the bears and their home. "The more people who see polar bears and understand their difficult situations, the better the chance we"ll alter our warming path in time to save them," he says.

单选题 Which is the best title for the passage?

单选题 Where do polar bears usually hunt seals?

单选题 The word "cubs" in the fourth paragraph is closest in meaning to ______.

单选题 According to the passage, which of the following statements is TRUE?

A、 Starving polar bears are increasingly coming into villages, where they may be killed either for food or safety.
B、 Polar bears can spend their entire lives on land if the sea ice melts completely.
C、 Two-thirds of the world"s polar bears may disappear by 2050 as global warming continues.
D、 The growing distance between ice packs is not a problem for polar bears, because they are excellent swimmers.

【正确答案】 C

【答案解析】事实细节题。A选项中提到北极熊因为饥饿而闯入村庄——coming into village，这个在原文中没有信息提到，所以排除。B选项中的spend their lives on land帮助我们定位到原文的第三段开头——polar bears can"t survive for long on land.与选项意思正好相反，所以排除。原文第二段最后一句That may cause two-thirds of the word"s 20,000 polar bears to be gone by then too.及前一句…the Arctic could be free of summer sea ice by 2050与C选项信息一致。原文第四段第三句话The bears must swim longer distances between ice packs(大片浮冰)，and they can"t always make it.与D选项中not a problem意思相左，因此排除。故选C。