What are the types of distributed operating systems?

c) Network Operating System is the correct answer.

While there are various architectural models within distributed systems (like client-server, peer-to-peer, etc.), the overarching term for an operating system that manages a network of computers is a Network Operating System (NOS).

Incorrect options:

Zone-based Operating System: This term doesn't have a standard definition in the context of operating systems.

Level-based Operating System: This term also doesn't have a standard definition in the context of operating systems.

Therefore, Network Operating System is the most accurate and widely recognized term for an operating system that manages a distributed system.