单选题 根据下面资料，回答问题。
A world like no other—perhaps this is the best way to describe the world of the rainforest. No rainforest is the same—yet most rain
forests can be found in the small land area 22.5 degrees north and 22.5 degrees south of the Equator （赤道）. You can find rain
forests in South America and Indo-nesia. Other rain
forests exist further from the Equator， in Thailand and Sri Lanka.
Rain
forests have a great role to play in supporting the world. They are home to a rich variety of plants， birds and animals. Can you believe that 480 varieties of trees may be found in just one hec-tare （公顷） of rainforest？ These forests have around 50% of all the plants， birds and animals on Earth.
Rain
forests have their own perfect way for living. The tall trees make a huge umbrella of bran-ehes and leaves which protect themselves， smaller plants， and the forest animals from heavy rain， dry heat from the sun and strong winds. Rainforest trees grow in such a way that their leaves and branches， although close together， never actually touch those of another tree. Scientists think this isa way to prevent the spread of any tree diseases and make life more difficult for leaf-eating insects（昆虫）. To live in the forest， animals must climb， jump， or fly across the branches and trees. The ground floor of the forest is not all leaves and bushes， like in films， but is actually fairly clear. It is where leaves become food for the trees and other forest life.
Rain
forests around the world are disappearing at a high speed. A few thousand years ago， rain-forests covered as much as 12% of the land surface on Earth， but today this has fallen to less than5.3%. We hope that the world governments work together with scientists to use their power and knowledge to keep the rain
forests for our existence. How much of the land surface on Earth is covered by rain
forests？