Forest is the cradle of human civilization and the ecological factor that most directly affects human survival. Forests absorb carbon dioxide and release oxygen to balance the proportion of atmospheric carbon dioxide. It is estimated that forests and plants in the world produce 400 billion oxygen annually Forests are rainmakers, which not only affect precipitation, but also reduce soil erosion on hillsides. This passage mainly supports the argument that the forest:. ['Is a rainmaker.', 'It is "natural oxygen bar".', 'is the cradle of human civilization.', 'is an important part of the human living environment.']