Final answer:
The activities of monitoring and managing service utilization and securing controlled access are described by the ITIL concept of 'warranty of a service' which assures the service meets agreed requirements.
Step-by-step explanation:
The activities described in the question pertain to the monitoring and management of IT service utilization and securing controlled access for users. These activities collectively ensure that the training provided by Foxfirst Consulting is available, reliable, and secure for its student subscribers. The most appropriate option that describes these activities is warranty of a service. Warranty in ITIL speaks to the assurance that a service will meet agreed requirements, this includes aspects such as availability, capacity, continuity, and security which are clearly being addressed through the monitoring and managing of service utilization, as well as securing and controlling access.