Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Rain forests cover less than six percent of the earth’s area, but they have 100,000 kinds of all the kinds of plants on the earth. Three-fourths of known kinds of plants and animals call the rain forest their home. Twenty percent of our different kinds of medicine comes from rain forests. The glues on an envelope and in shoes come from tropical plants. Rain forests provide materials for hundreds of other products.

Rain forests are also very important to the world’s climate. The Amazon rain forest alone receives about thirty to forty percent of the total rainfall on the earth and products about the same percentage of the world oxygen. Some scientists believe that the decreasing size of rain forests will affect the climate on the earth, making it uncomfortable or even dangerous for life.

Saving rain forests is an international problem. One country, or even a few countries, cannot solve the problem alone. The nations of the world must work together to find a solution before it is too late.

According to the passage, what must the nations of the world do to find a solution?