急性肾盂肾炎时作逆行肾盂造影目的是

A．除外梗阻是最重要的
B．因输尿管水肿而不能进行
C．可显示疾病所特有的异常
D．是不明智和得不出结果的
E．用于局部治疗是有用的

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. Another responsibility of a transport layer protocol is to create a  (2) and error-control mechanism at the transport level. TCP uses a sliding (3) protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve  (4) control. The transport layer is also responsible for providing a connection mechanism for the application program. The application program sends  (5) of data to the transport layer. It is the responsibility of the transport layer at the sending station to make a connection with the receiver.

空白（1）处应选择（）

A.numbers

B.connection

C.diagrams

D.resources