阅读下面短文，根据短文内容，完成表格中所缺信息，并将答案写在相应的横线上，每空限填一词。

Welcome to the Amazon rainforest. As the largest rainforest in the world, it plays an important role in keeping the balanced ecosystem（生态系统）on the Earth. With an area of around 6 million square kilometers, the Amazon rainforest is more than half the size of China. This area has a great many species（物种）. Actually, one in ten known species in the world can be found here.

Of the 390,000 plant species known to us, more than 40,000 can be found in the Amazon. There are different levels in the forest. At the bottom is a system of roots under the ground. Above that is leaf litter on the dark forest floor. The next level is made up of shorter plants with large leaves. Then there are the towering ancient hardwoods, and finally the tops of the trees which are taller than any other level of trees in the forest. Each level of the forest forms its own little world, home to different kinds of living things.

More than 1,300 species of birds and over 400 species of mammals（哺乳动物）hide among the forest’s plant life. This jaguar is one example. While a large number of jaguars survive here, they are only one part of this forest's food chain（食物链）. They feed on at least 87 species, including frogs. These frogs, in turn, feed on insects which eat leaves and fruit.

The Amazon rainforest is a treasure house of species that can be used for food or medicine. What’s more, the Amazon rainforest breathes life into the planet by producing over 20 percent of all the Earth’s oxygen（O₂）. So it is often known as the “lungs of the planet”.

The Amazon Rainforest
Introduction	The Amazon rainforest is the largest rainforest in the world, which helps keep the （1） of the Earth’s ecosystem.
Species	Plant species	Number: over 40,000 species
		Different levels in the forest: ●the bottom: a system of roots ●the second level: leaf litter ●the third level: shorter plants with large leaves ●the fourth level: towering ancient hardwoods ●the top: the tops of the （2） trees
	（3） species	Number: more than 1,300 species of birds and over 400 species of mammals
		One of the food chains in the forest: leaves and fruit→ （4） →frogs→jaguars
Importance	●The Amazon rainforest is a treasure house of species that can be used for food or medicine. ●Known as the “lungs of the planet”, the Amazon rainforest （5） over 20% of all the Earth’s oxygen.