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

This is the best experience I ________ in this city.
1. have had
2. have
3. had
4. will have
That is the second house they ________ this year.
1. buy
2. have bought
3. bought
4. had bought
The more we use private vehicles, ________ polluted the air becomes.
1. less and less
2. the less
3. the more
4. more and more
Life in rural areas is becoming ________ difficult for farmers because of falling prices of vegetables and argricultural products.
1. less and less
2. fewer and fewer
3. more and less
4. more and more