Choose the correct answer A, B, C, or D.

1. This is the best experience I ________ in this city.

A. have had                 B. have                       C. had                   D. will have

2. That is the second house they ________ this year.

A. buy               B. have bought                C. bought              D. had bought

3. The more we use private vehicles, ________ polluted the air becomes.

A. less and less             B. the less                  C. the more          D. more and more

4. Life in rural areas is becoming ________ difficult for farmers because of falling prices of vegetables and argricultural products.

A. less and less           B. fewer and fewer          C. more and less          D. more and more