Final answer:
TCP operates at the Transport layer of the TCP/IP model, ensuring reliable, ordered, and error-checked delivery between applications on an IP network.
Step-by-step explanation:
The Transmission Control Protocol (TCP) operates at the Transport layer of the TCP/IP model. This layer is responsible for maintaining end-to-end communication across the network. TCP provides reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts communicating via an IP network. It is one of the core protocols of the Internet protocol suite, often referred to as TCP/IP.
To put it simply, when you send an email or load a web page, for example, TCP works behind the scenes to ensure the data packets are sent and received without errors, in the correct order, and with no losses. It achieves this by establishing a connection between the sender and receiver, segmenting the data into smaller packets for transmission, and then reassembling the packets on the receiving end.
Therefore, the correct answer to the question is a) Transport.