填空题

Bears have long fascinated humans. Ancient cave art and more recent paintings and sculpture illustrate the fear as well as admiration with which people regard the awesome power and acute intelligence of bears. In fairy tales, bears are the symbolic image of brave deeds. In folk literature, the bear’s habit of disappearing in winter months and emerging in spring evokes a theme of spiritual renewal, the replenishment of food, and the return of prosperity. In modem times, as the recreational use of parks and wilderness areas has grown dramatically, humans have experienced increased contact with bears. Bear attacks on humans are rare, however. American black bears killed fewer than 40 people during the 20th century. Grizzly bears, a type of brown bear, are more dangerous, but attacks on humans are still rare. In United States national parks that are home to grizzlies, injury rates from grizzly bears are about one person per 2 million visitors. Bears prefer to avoid humans, but when attacks do occur, they are usually the result of humans surprising these nervous, shy, and easily frightened animals.
Bears are bulky animals with wide shoulders, a short back, short and thick legs, broad paws, and a short tail. They have an elongated head, rounded ears that stand straight up, small eyes, and a long snout. Bears hunt for food using an acute sense of hearing and an extremely keen sense of smell—some can detect odors from more than a mile away. Bear eyesight is probably similar in acuity (sharpness) to human vision. Black bears, and likely other bears, have color vision, which helps them identify ripe fruits and nuts.
The bear family includes eight species, each showing remarkable variation in physical features and habits. Some scientists believe that bears and animals in the raccoon family share a common ancestor and are more closely related to each other than to other carnivores. Other scientists believe that bears are more closely related to walruses and sea lions. In the past, zoologists placed the giant panda in the raccoon family, but recent analysis of the giant panda’s genetic makeup and fossil evidence have convincingly established the giant panda as a member of the bear family.
Bear fur color varies among species, ranging from all white, blonde, to black and white to all black or all brown.