Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks.

  We are using up the world’s petroleum. We use it in our cars and to heat our building in winter. Farmers use petro-chemicals to (23)…..the soil rich. They use them to kill insects eating plants. These chemicals go into rivers and lakes and kill the fish there. Thousands of pollutants also go into the air and pollute it. Winds carry this (24)…..air to other countries and other continents. Poor farmers use the same land over and (25)….. . 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 for firewood. In some areas when the trees are gone, the land (26)…..desert. Poor people can’t save the environment for the future. 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.

Farmers use petro-chemicals to (23)…..the soil rich.