IV. Write the correct form of the words in brackets. 16. As the world’s population increases, there is less land _________ for agriculture to feed all the people. (LEAVE) 17. We participate in a lot of activities to help the _________ people in the countryside. (OLD) 18. Natural gas is _________ and it is harmful to the environment. (LIMIT) 19. He was still _________ when I saw him at 11 o’clock yesterday evening. (WAKE) 20. Traffic accidents can be _________ if people obey the rules. (PREVENT)