Inside the computer, the operation system (of another software module called a data communication (71) )must decide which program will get control next. Each program remember, is associated (72) . a particular front -end port. If a program’s data have not yet reached its front - end buffer, there is no point giving that program control. Thus the data communication monitor sends its own (73) signal to the front -end devices next port is polled. Note that the (74) computer speed. The computer never has to wait for a terminal or a communication line. Instead, it is the expressive front - end processor that waits for the slower system (75) to respond.

（72）处填（）。

A.with

B.on

C.in

D.upon

在Quidway路由器中的IPX协议支持（）封装格式

A、Ethernet_II

B、Ethernet_snap

C、Ethernet_sap

D、Ethernet_802.2

E、Ethernet_802.3

F、Ethernet_802.5