Read the following passage and mark the letter A, B, C or D on the answer sheet to indicate the correct answer to each of the questions from 23 to 27.

 

Tropical forests have supplied us with many sorts of plants for food, medicine and industry. They can probably supply man much more. They also reduce floods and droughts, keep water clean, and slow down the Greenhouse Effect. However, the tropical forests are being destroyed to make rooms for things like farms and fields. Besides, forest fires are the most terrible destruction. About 20 million hectares are lost annually - an area which is twice as big as that of Australia. The World Wildlife Fund (WWF) is working to protect and save the forests that are in danger, to plant new trees for fuel wood and to slow down the Greenhouse Effect. It encourages governments and people to do something for the sake of the tropical forests.

What is the main purpose of the writer when writing this passage?