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问题 单项选择题

固定式螺旋千斤顶在重物的作用下，螺杆不会转动而使重物下降是因为（）。

A．重物起升后人为用销轴，将重物锁死在顶升的高度；

B．千斤顶的螺纹导角小于螺杆与螺母间的摩擦角，具有自锁作用；

C．在千斤顶的螺杆和壳体间具有一卡位系统，将螺杆卡死在某一高度；

D．通过两块闸瓦将螺杆抱紧；

答案

参考答案：B

多项选择题

有关淋菌的临床表现，下列哪些正确（）

A.潜伏期长达3～5周

B.可引起子宫内膜炎、输卵管炎

C.妊娠早期淋菌性宫颈管炎可致感染性流产

D.淋菌可隐匿存在于生殖器分泌物中

E.以上都不是
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单项选择题

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.

71（）

A．interval

B．time

C．slot

D．delay
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