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

下列关于犯罪未遂、犯罪中止的关系说法正确的有()

A.未遂是由于犯罪分子意志以外的原因未得逞。中止是在犯罪过程中，犯罪分子自动放弃犯罪或自动有效的防止犯罪结果之发生

B.是否着手不同

C.犯罪未遂可有预备未遂，犯罪中止则无

D.有无犯罪结果不同

E.自动防止犯罪结果的情况下，既有可能成立犯罪未遂，也有可能成立犯罪中止