What are the 4 functions of ITIL's?

The correct answer to this question is B. It is likely that a service desk will be responsible for logging details of incidents and service requests, providing first-line investigation and diagnosis, and restoring service. They are the first place the customer or user is going to contact in case of a problem, and they need to figure out what is going wrong and how to fix it for the client.

Although diagnosing the root-cause of problems is also important, this is likely done by a member of another team who specializes in this diagnosis and can spend more time researching and identifying the underlying issue.