How should files be properly maintained to ensure their effectiveness?

Maintaining files effectively is crucial for their longevity and performance. The correct answer highlights the practice of using a quick blow on a wood block to unclog the teeth of the file. This method serves to remove debris and buildup that can accumulate in the file's teeth after use, allowing for smoother operation and preventing damage to the file itself. Regular maintenance like this helps keep the file sharp and effective, ensuring it continues to perform its intended function efficiently.

The other options presented do not align with best practices for file maintenance. Regularly oiling files and storing them in a damp place could lead to rust and deterioration, while infrequent use with minimal cleaning would allow for buildup, resulting in reduced effectiveness. Using files solely on metal surfaces limits their versatility and can wear them down quicker than recommended usage, particularly if they are not maintained properly through cleaning and care.