Answer: Option 3Concept: Transport Layer:It performs the same functions as that of the transport layer present in the OSI model. Here are the regarding the transport layer:It uses TCP and UDP protocol for end-to-end transmission.TCP is a reliable and connection-oriented protocol (In OSI Stack).TCP also handles flow control.The UDP is not reliable and a connection-less protocol also does not perform flow control.Protocols utilized in this layer: TCP/IP and UDP protocols are deployed in this layer.Explanation: 1. Real-Time Multimedia: For real-time multi-media applications the packets must be delivered faster if some packets are lost in between that is ok with these particular types of applications. Hence UDP will work just fine for these applications.2. File Transfer: for file transfer applications generally used FTP. FTP also relies on TCP.3. Domain Name Server: DNS generally employs UDP as its underlying transport layer protocol. ( at Some places it also uses TCP but we have to choose the best possible answer among the available options)4. E-mail: Email employs SMTP which also uses TCP.Hence Option 3 is the correct answer.