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

We are using up the world’s Petroleum. We use (18) _______ in our cars and to heat our building inwinter.Farmers use petrochemicals to (19)_______ the soil rich. They use them to kill insects (20) _______ eat plants. These chemicals go (21)_______ rivers and lakes and kill the fish there. Thousands of pollutants also go into the air and pollute it. Winds carry this (22)_______ air to other countries and other continents.

Poor farmers use the same land over and (23)_______. The land needs a rest so it will be better next year. However, the farmers must have food this year. Poor people cut down forests (24)_____ firewood. In some areas when the trees are gone, the land (25)_______ desert. Poor people can’t save the environment for the (26)_______

This is not a problem for one country or one area of the world. It is a problem for all- humans. The people and the nations of the world must work together to (27)_______ the world’s resources.

Điền vào số (20)

I have told you not to do it _______. A. hundreds of times