离散程度的测度，主要包括（）。

A.极差

B.方差

C.标准差

D.离散系数

E.误差

TCP/IP (21) layer protocols provide services to the application (22) running on a computer. The application layer does not define the application itself, but rather it defines
(23) that applications need — like the ability to transfer a file in the case of HTTP. In short, the application layer provides an (24) 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 (25) layer consists of two main protocol options — the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).

A. application B. transport C. link D. network