To solve this question, the user needs to know the basic concepts of hard disk allocation. When a file is stored on a hard disk, the operating system needs to know where on the disk to store it. The hard disk is divided into smaller sections, and the operating system allocates these sections to files as needed. These sections are known as allocation units.

Now, let's go through each option and explain why it is right or wrong:

A. Cylinders: This option is correct. A cylinder is a group of tracks on a hard disk that are located at the same position of the disk's read/write head. Cylinders are used to allocate space on older hard disks.

B. Tracks: This option is correct. A track is a circular path on a hard disk that is used to store data. Tracks are used in conjunction with cylinders to allocate space on older hard disks.

C. Blocks: This option is correct. A block is a group of sectors on a hard disk that are allocated as a unit. Blocks are used to allocate space on modern hard disks.

D. All of the above: This option is correct. All of the options listed (cylinders, tracks, and blocks) are used to allocate space on hard disks.

E. None of the above: This option is incorrect. All of the options listed (cylinders, tracks, and blocks) are used to allocate space on hard disks.

The Answer is: D