Which tool encrypts entire drives, rendering them unusable unless one possesses the correct key to unlock the drive?

Whole disk encryption.

Explanation:

Whole disk encryption, also known as, the full disk encryption is a tool that encrypts the entire drive. The whole disk encryption protects the whole hard drive from unwanted visitor to enter into your system.

This tool protects your entire data, softwares, files, etc stored in the hard drive. Whole disk encryption cedes the entire hard drive unusuable untill correct key is entered to unlock the drive.

Thus the correct answer is 'whole disk encryption.

answer; i believe its aptitude;