A、15%. B、10%. C、About 50%. D、Nearly 30%. C题目问热带雨林包含了世界上多少植物品种。短文中提到"They cover less than 10% of the world’s land，but they contai

Human beings are cutting down the world’s rain forests at the rate of 20 hectares a minute (31) . Every year, 30 million hectares of rain forests are destroyed. And at this rate, most of the world’s rain forests will disappear very soon.
    The forests are cut down sometimes for wood, sometimes for farms so that crops and vegetables can be planted and sometimes to make way for roads. But the forests do not re-grow. The soil is very thin and it is soon washed away by the rain. The land is then too poor for the forests to begin to grow again.
    There are a number of good reasons for saving the rainforests. Several important drugs in hospitals have come from the rain forests. Also they produce food. The rain forests are rich in wildlife, too. They cover less than 10% of the world’s land, but they contain 40%～50%of the world’s species of plants and animals (29) . The trees supply oxygen.  If the rain forests are destroyed, this will change the world’s weather (30) . Temperatures will go up, sea levels will rise and there will be changes in rain and snowfall.
    Today, research studies in forests in Panama, New Guinea and Indonesia may help us to find solutions to save the world’s rain forests.