Have you ever entered a tropical rainforest(热带雨林)？Rainforests make up only a small part of the Earth's surface, aboutsix percent, but there are more kinds of trees than any other area in the wholeworld.
Tropical rainforests are in Africa, Asia, Central and SouthAmerica, Australia, and on the Pacific Islands. The largest tropical rainforestis the Amazon (亚马逊) Rainforests in South America, which covers 1.2 billion acres, oralmost five million square kilometers. The second largest rainforest is inWestern Africa.
Rainforests provide us with many things. In fact, the AmazonRainforest is the "lungs of our planet" because it produces 20% ofthe world's oxygen(氧气). One fifth of the world's fresh water is found in the AmazonRainforest. Furthermore, one half of the world's species of animals, plants andinsects live in the Earth's rainforests. 80% of the food we eat first grew inthe rainforest. 25% of the drugs we take when we are sick are made of plantsthat grow only in rainforests. Some of these drugs are often used to fight andcure cancer.
There are four different levels of trees in a rainforest. Theforest floor is the lowest layer full of animal life and receives theleast amount of light. The understorey is the dark, coolenvironment under the leaves but over the ground. The canopy layeris the upper parts of most of the trees. The emergent layercontains a small number of very tall trees.
These different parts of a rainforest exit(生存) together to createan ecosystem for many animals, plants and human beings.
B . 
C . 
D . 
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