Arctic Circle where the polar bears has reduced in size (21)_________ about 30 per cent

Câu hỏi :

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 21 to 25.

Polar bears are in danger of dying out. Unlike some other endangered animals, it's not hunters that are the problem, it's climate change. Since 1979, the ice cap at the Arctic Circle where the polar bears has reduced in size (21)_________ about 30 per cent. The temperature in the Arctic has slowly been rising and this is (22)_________ the sea ice to melt, endangering the polar bears' home. The polar bears' main sources of food are the different types of seals found in the Arctic. They catch them by waiting next to the air holes seals have made in the ice. (23)_________ the bears are very strong swimmers, they could never catch seals in water. This means that the bears really do rely on the ice to hunt.

Polar bears also need sea ice to travel. They can cover a huge territory and often swim from one part of the ice to another. They have been (24)_________ to swim up to 100 km, but when there is less ice, they may have to swim further and this can (25)_________ fatal to the bears. A number of bears have drown in the last few years and scientists believe that it is because they were not able to reach more ice before they became too tired and couldn't swim any further.