In ITIL 4, the service desk practice is defined as the single point of contact between the service provider and its users. One of its key responsibilities is to ensure that:

Users can contact the service provider easily

There are multiple communication channels available (phone, email, chat, self-service portal, mobile app, etc.)

Calls, messages, and contacts from users about incidents, service requests, and inquiries are captured and handled

This means the service desk is the practice that guarantees users have a range of access channels to report problems and requests.

Why the other options are not correct:

B. Service level managementFocuses on setting, agreeing, and managing service level targets and ensuring that services meet agreed performance levels. It does not primarily manage user contact channels.

C. Incident managementFocuses on restoring normal service operation as quickly as possible after incidents occur. It uses information gathered by the service desk but does not itself guarantee multiple channels for users.

D. Change enablementDeals with ensuring that changes are properly evaluated, authorized, and managed. It is not about user-facing communication channels.

Therefore, A. Service desk is correct because it is explicitly responsible for providing and managing the channels through which users report issues and make requests.

References (ITIL 4 Foundation):

ITIL® Foundation: ITIL 4 Edition – Service desk practice (purpose and key activities)

ITIL® Foundation: ITIL 4 Edition – Overview of incident management and relationship with the service desk