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