热继电器可作为一般电动机的过负载保护。

The network layer provides services to the transport layer．It can be based on either (71) ．In both cases，its main job is (72) packets from the source to the destination．

In network layer，subnets can easily become congested，increasing the delay and (73) .

for packets．Network designers attempt to avoid congestion by proper design．Techniques include (74) policy，caching，flowcontrol，and more．

The next step beyond just dealing with congestion is to actually try to achieve a promised quality of service．The methods that can be used for this include buffering at the client，traffic shaping，resource (75) ，and admission control．Approaches that have been designed for good quality of service include integrated services(including RSVP) ，differentiated services， and MPLS．

（73）处填（）。

A．lowering the throughput

B．lowering the correctness

C．lowering the effectiveness

D．lowering the preciseness

异丙肾上腺素的作用是

A．β₁肾上腺素受体激动剂
B．β₂肾上腺素受体激动剂
C．α₂肾上腺素受体激动剂
D．β₁＞β₂肾上腺素受体激动剂
E．β₂＞β₁肾上腺素受体激动剂

Thank you for your timely help; otherwise we _______ in great trouble now.

A．are

B．would have been

C．would be

D．were

一个多匝闭合矩形线圈在匀强磁场中匀速转动，产生的交流电的电动势表达式为（V），则下列判断正确的是：

A．该交电流的频率为50Hz

B．通过该矩形线圈磁通量的最大值为100Wb

C．该交电流电动势的有效值是100V

D．1s内该交流电电流的方向变化50次

下颌牙列中按牙周膜面积从大到小的排列顺序是（）

A.6753412

B.7635412

C.6734521

D.7654321

E.6754321