c. Service
A service is a program loaded into memory that has no user interface, but communicates with other programs. Services are typically used to perform background tasks or provide functionality to other programs. They are often used to manage system resources, such as network connections or hardware devices. Examples of services include the Windows Event Log service, the Print Spooler service, and the Task Scheduler service.
A process is a program that is currently running in memory and can have a user interface.
A task is a set of instructions that tells the operating system what needs to be done, it can be a process or a service.
An application is a program that runs on a computer and has a user interface.