工业革命的标志性成就是瓦特改进蒸汽机，把人类带入“蒸汽时代”，由此带来的影响是

①生产力获得巨大发展②社会面貌发生巨大变化

③使资本主义最终战胜封建主义④使美国成为世界头号经济大国[ ]

A．①②③

B．②③④

C．①②④

D．①③④

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

In low-speed network, it is usually adequate to wait for congestion to occur and then react to it by telling 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 offered and the service expected.

73（）

A．collision

B．congestion

C．drop

D．delay