III. Choose the best answer 16. ________we find new sources, we will soon run out of energy. A. If B. When C. Unless D. Only 17. All of our rain forests ________ unless we find some ways to stop people from cutting down tree. A. will be destroyed B. are destroyed C. will destroy D. destroy 18. Unless we ________ throwing garbage into the river, it will be polluted. A. stop B. don’t stop C. will stop D. won’t stop 19. The pollution rate in this area seems ________ slowly. A. increase B. increasing C. to increase D. to be increase 20. ________ it rained a lot, we enjoyed our holiday. A. Because B. Despite C. Although D. Because of