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).
（75）处填（）。
A．application
B．session
C．physical
D．transport
