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．

（72）处填（）。

A．packets

B．cells

C．message

D．files

在必须具备( )条件情况下，行政行为才能产生法律效力。

A．行为的主体、行为的客体、行为的内容、行为的程序、行为的形式

B．行为的形式、行为的精神、行为的艺术、行为的主体、行为的客体

C．行为的艺术、行为的内容、行为的主体、行为的客体、行为的结果

D．行为的内容、行为的艺术、行为的结果、行为的形式、行为的主体