IEEE802.3标准，定义了CSMA/CD总线介质访问控制子层与 ______。A

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 (1) between sending the notification and notification arriving at the source, thousands of additional (2) may arrive. In ATM network, a major tool for preventing (3) is (4) control. When a host wants a new virtual (5) , it must describe the traffic to be offered and the service expected.

5（）

A．path

B．rout

C．circuit

D．way

某企业投保企业财产综合险，固定资产按照账面原值投保，保险金额为100万元。在保险期间内，因山洪导致该企业房倒屋塌、机器设备受损，损失达50万元。出险时，其固定资产重置价值为200万元。保险公司的赔偿金额为( )。

A．75万元

B．25万元

C．62.5万元

D．50万元

电缆沟、地沟，按设计图示以( )计算。

A．中心线长度

B．面积

C．体积

D．深度

如图所示，A、B两物块叠放在光滑水平面上，用水平力F拉A时，A、B间无相对滑动，A、B间摩擦力为f；用同样的水平力F拉B时，A、B间也无相对滑动，而其间摩擦力变为f '，设A、B质量分别为m_A、m_B，则f:f '为(    )

A．1:1            B．m_A:m_B

C．m_B:m_A             D．

B/L is the abbreviation for _________.

A．letter of credit

B．buying contract

C．commercial invoice

D．bill of lading