There are many reasons for animals dying out, but the most important one is the part that humans have played. First, many animals have been killed for food. Second, many of the places where animals used to live have been destroyed.

　　Wet land has been turned into field. More and more trees in the forests have been cut down, but few trees are planted. Much land has either been changed into agricultural land or used for building factories and houses. Polluted rivers and lakes have also been a cause of death of some of the animals.