采用ABC法对存货进行控制时，应当重点控制的是( )。

A．数量较多的存货

B．占用资金较多的存货

C．品种较多的存货

D．库存时间较长的存货

A transport layer protocol has several responsibilities. One is to create a process-to-process (program-to-program) communication; TCP uses port （） to accomplish this. Another responsibility of a transport layer protocol is to create a （） and error-control mechanism at the transport level. TCP uses a sliding （） protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve （） control. The transport layer is also responsible for providing a connection mechanism for the application program. The application program sends （） 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.

The application program sends （） of data to the transport layer.

A．ports

B．streams

C． packets

D．cells