The correct answer is A. regular backups.
Regular backups are the best way to protect your hard drive data because they create a copy of your data that can be restored if your hard drive fails. There are many different ways to back up your data, including using a cloud storage service, an external hard drive, or a USB drive.
Option B, periodically defragmenting your hard drive, can help to improve the performance of your hard drive, but it will not protect your data from loss. Option C, running chkdsk at least once a week, can help to identify and fix errors on your hard drive, but it will not protect your data from loss. Option D, running scandisk at least once a week, is similar to chkdsk, but it is not as widely used. Option E, running a regular diagnostic, can help to identify problems with your computer, but it will not protect your data from loss.
In addition to regular backups, there are other things you can do to protect your hard drive data, such as using a surge protector to protect your computer from power surges, and keeping your computer clean and free of dust.