TCP/IP (1) layer protocols provide service

问题：

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（5）处应选择（）

A.application

B.session

C.physical

D.transport