Found only in Africa，hippos come in two varieties.The small pygmy hippo lives in rain forests.And the large common hippo lives mostly in grassland around rivers and lakes.

　　The common hippo is the third largest land mammal in the world.It is lighter than the largest of the white rhinos and the elephant，the heaviest land animal.The elephant is almost twice as heavy as the common hippo.

　　In the past，the hippo has been killed for meat，for sport，and for its tough skin.But today，in preserves only，the common hippo has increased in number.The hippo has few predators(天敌) other than lions and leopards that sometimes catch young hippos.There were many hippos killed by man during the last half of the 19th century，when Africa was being explored and settled.And a great many hippos and other animals were killed by poachers(偷猎者) during the fighting in Uganda in the 1970s.The hippo is strong，though.It resists disease and has a long lifetime，living 20 to 40 years in the wild.

　　Hippos spend most of their time in the water，only moving onto land at night to eat.By feeding at night，their skin is protected from the sun and the dry air that can cause a serious loss of moisture(水分)．

　　Because of its large body，the common hippo may appear awkward on land，but it can move very fast and is considered by many to be the most dangerous animal in Africa.By spending their days in the water and their nights on land，hippos make it difficult for scientists to study them，so there is still much to be learned about hippos.The huge hippos，with their big mouths and tiny ears，have always fascinated humans.As scientists learn more about them，they become even more fascinating.

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