In low-speed network，it is usually adequate to wait for congestion to occur and then react to it bytelling the source of packets to slow down．In high-speed networks，this approach often works poorly，because in the (71) between sending the notification and notification arriving at the source，thousands of additional (72) may arrive．In ATM network，a major tool for preventing (73) is (74) control．When a host wants a new virtual (75) ，it must describe the traffic to be offeredand the service expected．

（74）处填（）。

A．flow

B．admission

C．traffic

D．time

三相异步电动机定子绕组串接电阻降压启动控制就是让电动机启动时在定子绕组和电源之间（）电阻。