The suggested answer is A.
TCP and UDP are both transport layer protocols in computer networks, but they differ significantly in how they establish and maintain connections. TCP (Transmission Control Protocol) uses a three-way handshake to establish a connection, which involves SYN, SYN-ACK, and ACK packets to synchronize and acknowledge receipt of connection requests. In contrast, UDP (User Datagram Protocol) is a connectionless protocol that does not guarantee message delivery or establish connections through a handshake process. Thus, TCP is used when reliable communication is essential, while UDP is used for faster, simpler messaging where occasional loss is acceptable.