正解:D
The transport layer is the fourth layer of the OSI model, and it is responsible for end-to-end delivery of data over a network. It uses standard protocols such as TCP, UDP, and DCCP to enhance its functionalities. One of the main functions of the transport layer is to ensure that messages are transmitted to their destinations reliably and in the correct order. It also prevents data duplication by using sequence numbers, acknowledgments, and retransmission mechanisms