【正确答案】 B

【答案解析】The Nile crocodile has a somewhat deserved reputation as a vicious man-eater. The proximity of much of its habitat to people means run-ins are frequent. And its virtually indiscriminate diet means a villager washing clothes by a riverbank might look just as tasty as a migrating wildebeest. Firm numbers are sketchy, but estimates are that up to 200 people may die each year in the jaws of a Nile crocodile. Africa's largest crocodilian, these primordial brutes reach a maximum size of about 20 feet (6 meters) and can weigh up to 1,650 pounds (730 kilograms). Average sizes, though, are more in the range of 16 feet (5 meters) and 500 pounds (225 kilograms). They live throughout sub-Saharan Africa, the Nile Basin, and Madagascar in rivers, freshwater marshes, and mangrove swamps. Nile Crocodiles1 brains and hearts are more advanced than those of any other living reptiles. They have changed little in 65 million years. In contrast lizards, they have a "high walkM. They swim with their tails, but their hind feet are webbed and can be used to submerge quickly. Crocodiles are not solitary predators as often imagined, but social creatures. Cows of some species protect not only their hatchling young but offspring from the previous year. Nile crocodile bulls also respond to distress calls of their young. Crocodiles convey social messages with motions, odors, postures, by touch and with sounds. Nile Crocodiles produce at least six different vocal signals. Both cow and bull Nile Crocodiles maintain territories, especially during breeding season. Nile crocodiles have voracious appetites. They feed on animals which come to the water to drink. These include zebras, hippos, wildebeest, porcupines, pangolins, and birds. They feed mainly on fish, including the barbel catfish. They will also eat other crocodiles and carrion. They sometimes team up to hunt. When an animal comes to the riverbank, the Nile crocodile attacks it, seizing the animal and dragging it underwater until it drowns. It cannot chew, so the prey is stuck underneath a log to rot. Nile crocodiles eat the entire animal, including bones, antlers, etc. Pebbles are sometimes swallowed to aide in digestion. They have been known to attack man. They have a slow metabolism. Nile Crocodiles were once widely distributed over Africa south of the Sahara and on offshore islands. Their present range is smaller and they have become endangered because of habitat destruction and the value of their leather. The Nile crocodiles, in particular, have been a source of highly durable leather for a variety of products which can be crafted and manufactured, such as purses, shoes and other leather protects primarily sold in the United States, Europe and East Asian countries such as Italy, France and Japan, respectively. Commercial utilization is generally on a large scale involving large number of people. Between the years 1950-1980, it was estimated that approximately three million crocodiles were killed for their skins. Natives also use crocodile parts as a part of their culture for decorations on ceremonial accessories. Crocodile parts have also been used by natives in sacrificial rites. Moreover, crocodile meat is eaten by tribal people in Tanzania and especially in Western Africa. Recently, crocodiles have been used for meat and meat products for human consumption outside of tribal regions. Skeletal bones and osteoderms of the crocodile are being used for nutritional supplements in agriculture and animal feeds, and teeth and claws are being sold primarily to tourists as curios. In addition, crocodiles have been used for medicinal purposes. The body fat and oil of crocodiles is believed to cure skin ulcers, burns and respiratory ailments. The news of the healing powers of crocodile fat and oil has spread to other countries and the demand for these medicines is increasing. Due to increasingly adverse environmental pressures and populations that have encroached on crocodile habitats and the over utilizing of crocodiles for commercial exotic leather trade, crocodiles have been close to extinction.