Which command is used to delete all the files in the root directory of drive a

Del . a: is the command used in DOS to delete all files in the root directory of drive A.

Explanation:
The del command is used to delete files in DOS.
. specifies that all files (regardless of their extensions) should be deleted.
a: specifies the drive letter A, indicating that the operation should be performed on drive A (the floppy disk drive).

When you execute del . a: at the DOS prompt, it will delete all files in the root directory of the A drive.

A:\del is not the correct syntax for deleting all files on drive A. The correct command starts with del followed by . and the drive letter.

Del a: is incorrect because it doesn't specify the files to delete (missing . or specific file names).

Erase . is not a valid command in DOS for deleting files. The correct command is del for deleting files.

Therefore, the correct answer is Option B: Del . a:.