TCP/IP (1) layer protocols provide services to the application (2)running on a computer. The application layer does not define the application itself, but rather it defines(3)that applications need - like the ability to transfer a file in the case of HTTP. In short, the application layer provides an (4)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 (5)layer consists of two main protocol options - the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).
空白（4）处应选择（）
A.iteration
B.object
C.interface
D.activity