Final answer:
The OSI Model's Transport Layer is the correct answer, since TCP and UDP are protocols operating at this level, allowing communication between servers and clients.
Step-by-step explanation:
The question relates to the OSI Model, which defines different layers by which computer systems can communicate over a network. Given the terms Transport Control Protocol (TCP), Client-Server, Server, and User Datagram Protocol (UDP), these are all related to the C) Transport Layer of the OSI Model. The Transport Layer is responsible for providing communication services directly to the application processes running on different hosts within a layered architecture of protocols and other network components.