图3-3所示的UML类图描绘的是设计模式中的______模式。图3-4所示的UML类图描述了该模式的一种应用，其中与图3—3中的“Abstraction”对应的类是______。

A．Composite(组合)
B．Proxy(代理)
C．Bridge(桥接)
D．Command(命令)

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