To solve this question, the user needs to know how to track disk space use on a per-user basis without denying users access to a volume.

Option A: Enable disk quotas. This option is correct because disk quotas allow administrators to track disk space use on a per-user basis. Disk quotas can be set to limit the amount of disk space a user can use, but they do not deny users access to a volume.

Option B: Enable disk quotas and set the disk quota warning level. This option is incorrect because setting the disk quota warning level only notifies users when they are approaching their disk quota limit. It does not allow administrators to track disk space use on a per-user basis without denying users access to a volume.

Option C: Enable the disk quota warning level only. This option is incorrect because enabling the disk quota warning level only notifies users when they are approaching their disk quota limit. It does not allow administrators to track disk space use on a per-user basis without denying users access to a volume.

Option D: Disable disk quotas. This option is incorrect because if disk quotas are disabled, administrators will not be able to track disk space use on a per-user basis.

Therefore, the correct answer is: The Answer is: A (Enable disk quotas).