Please choose the correct solution to the question: How often should air filters be cleaned or replaced?

Solution1: 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.

Solution2: 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 format: solution1/solution2
Answer: solution1