MAC is used for:

A.
Defining imposed access control level.

B.
Defining user preferences.

C.
None of the choices.

D.
Defining discretionary access control level.

Explanation:
As the name implies, the Mandatory Access Control defines an imposed access control
level. MAC is defined as follows in the Handbook of Information Security Management:
With mandatory controls, only administrators and not owners of resources may make
decisions that bear on or derive from policy. Only an administrator may change the
category of a resource, and no one may grant a right of access that is explicitly
forbidden in the access control policy.