Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions

Melting of sea ice in the Arctic has reduced the population size of polar bears and threatens the species with extinction. Scientists say that the earlier annual break-up of sea ice caused by climate change is cutting short the hunting season for the bears, which depend on floating banks of ice to reach their prey.
Lack of sea ice in spring and summer is forcing the hungry polar bears to spend longer on land. This gives a false impression that their numbers are increasing as they encroach on human settlements to search for food.
Female polar bears depend on the spring hunting season in order to build the fat reserves needed to see them through the summer months. But the ice is disappearing, which means that the bears have not had time to build up normal levels of fat. Since female bears become thinner, they are easily affected by disease. Their ability to reproduce and the survival chances of their cubs decline significantly.
The sea ice provides polar bears with a hunting ground, from which the bears can reach their prey-wild seals and other marine mammals. Scientists are worried that if the sea ice season continues to get shorter, polar bears will not be able to spend enough time on the ice to hunt and feed themselves.

Câu hỏi

The word "they" in in paragraph 3 refers to _______.