TCP/IP (71) layer protocols provide services to the application (72) running on a computer. The application layer does not define the application itself, but rather it defines (73) that applications need-like the ability to transfer a file in the case of HTTP. In short，the application layer provides an (74) between software running on a computer and the network itself．The TCP/IP application layer includes a relatively large number of protocols，with HTTP being only one of those．The TCP/IP (75) layer consists of two main protocol options-the Transmission Control Protocol(TCP)And the User Datagram Protocol(UDP)．
A．application
B．session
C．physical
D．transport
