产生（）的主要原因是电气设备载流部分的绝缘破坏。A.短路 B.断线 C.不对称故障

某同学在研究电容、电感对恒定电流与交变电流的影响时，采用了如图所示的电路，其中L₁、L₂是两个完全相同的灯泡，把开关置于3、4时，电路与交流电源相通，稳定后的两个灯泡发光亮度相同，则该同学在如下操作中能观察到的实验现象是（　　）

A．当开关置于l、2时，稳定后L₁亮、L₂不亮

B．当开关置于l、2后，L₁、L₂两个灯泡均不发光

C．当开关从置于3、4的状态下突然断开，则两灯泡同时立即熄灭

D．当开关刚置于3、4的瞬间，L₂立即发光，而L₁亮度慢慢增大

学习和教学的过程包括学习过程、教学过程和_________。

We have already covered the topic of network addresses. The first （） in a block (in classes A，B，and C) defines the network address. In classes A，B，and C，if the hostid is all ls， the address is called a direct broadcast address. It is used by a.（） to send a packet to all hosts in a specific network. All hosts will accept a packet having this type of destination address. Note that this address can be used only as a （） address in an IP packet. Note also that this special address also reduces the number of available hostid for each netid in classes A，B，and C.

In classes A，B，and C，an address with all is for the netid and hostid (32 bits) defines a（） address in the current network.A host that wants to send a message to every other host can use this address as a destination address in an IP packet. However，a router will block a packet having this type ofaddress to confine the broadcasting to the （） network. Note that this address belongs to class E.

It is used by a.（） to send a packet to all hosts in a specific network.

A．router

B．switch

C．hub

D．firewall

正常情况下，配电箱、开关箱在使用过程中的停电先后顺序是（）。

A．总配电箱→分配电箱→开关箱

B．开关箱→分配电箱→总配电箱

C．分配电箱→总开关箱→开关箱

D．总开关箱→分配电箱→开关箱

工程咨询业的特点包括( )。

A．咨询任务弹性大
B．时效性强
C．以智力活动为中心
D．咨询成果是预测性的
E．咨询任务具有类似性，重复性