Write the correct form of the words in brackets

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