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．

（71）处填（）。

A．interval

B．time

C．slot

D．delay

填写第一种工作票的范围是（）

A、在高压设备上工作需要全部停电或部分停电者

B、在控制盘和低压盘配电箱电源干线上的工作

C、二次回路上的工作，无需将高压设备停电者

D、在高压室内的二次线和照明等回路上的工作，需要将高压设备停电或做安全措施者