A transport layer protocol has several responsibilities, One is to create a process-to-process (program-to-program) communication; TCP uses port （1） to accomplish this. Anotherresponsibility of a transport layer protocol is to create a（2）and error-control mechanism atthe transport level. TCP uses a sliding（3）protocol to achieve flow control. It uses theacknowledgment packet, time-out, and retransmission to achieve （4） control. The transportlayer is also responsible for providing a connection mechanism for the application program. Theapplication program sends （5）of data to the transport layer. It is the responsibility of thetransport layer at the sending station to make a connection with the receiver.

（5）是（）

A.ports

B.streams

C.packets

D.cells

下列关于水泵接合器说法正确的有（）。

A、分为地上式、地下式和边墙式

B、阀件采用法兰连接

C、其安装位置应有明显标志，附近不得有障碍物

D、止回阀安装方向准确，由室内流向室外