Finish the following sentence with the best choice: How often should air filters be cleaned or replaced?

Choices:
- Air filters should be checked monthly and cleaned or replaced when it appears dirty. For the best results, change the filter after no longer than 90 days.
- Air filters only need to be replaced twice a year. Air filters should be replaced once in the winter and once in the summer.

Answer:
Air filters should be checked monthly and cleaned or replaced when it appears dirty. For the best results, change the filter after no longer than 90 days.