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．

（73）处填（）。

A．collision

B．congestion

C．drop

D．delay

图表式窗体中出现的字段不包括( )。

A．系列字段

B．数据字段

C．筛选字段

D．类别字段