【判断题】
三相异步电动机的转速取决于电源频率和极对数，而与转差率无关。
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相关试题
【判断题】
三相异步电动机旋转磁场的旋转方向是由三相电流的相序决定的。
【判断题】
164·劈相机启动时应投入启动电阻后方能启动，当劈相机启动完成后必须切除启动电阻。
【判断题】
劈相机可实现单一三相供电系统的电压以及电流的对称供电特性。
【判断题】
166·旋转劈相机可自动启动而无需启动控制。
【判断题】
旋转劈相机是将单相交流电劈成三相交流电的装置。
【判断题】
168·电力机车运行方向的控制，采用改变牵引电动机电枢绕组的电流方向实现的。
【判断题】
电力机车运行中若要改变方向，必须在机车停车后才能转换。
【判断题】
170·电力机车上电器采用的冷却方式为风冷。
【判断题】
172-碱性蓄电池充电过程中，电解液密度升高。
【判断题】
175·当代铁路机车三大高科技技术：交直流传动技术、微机控制技术和径向可调节转向架技术(径向自导向轮对)。
【判断题】
176·继电器是辅助电路中主令电器和执行电器之间进行逻辑转换及传递的控制电器。
【判断题】
177·继电器是一种根据输入量变化来控制输出量跃变的自动电器，可以实现控制、保护有关电器设备。
【判断题】
电流继电器的动作值整定可通过改变反力弹簧拉力来实现。
【判断题】
电流继电器的动作值整定是通过改变铁芯气隙来实现的。
【判断题】
180·TJJ2系列继电器的磁系统为吸合式并带有吸引线圈，指示器带有恢复线圈及螺管式磁路。
【判断题】
181·电流继电器是用于电动机的过载及短路保护，直流电机的磁场控制或失磁保护等场合。
【判断题】
触头的触头压力就是两触头接触后的压力。
【判断题】
触头的初压力可以防止触头接触时的碰撞。
【判断题】
触头的开距必需保证触头经的住电压的冲击而不被击穿。
【判断题】
触头的开距、超程、压力都是检修中必须进行检测的主要参数。
【判断题】
真空接触器具有耐压强度高，介质恢复数度快，接通、分断能力大，电器和机械寿命长等优点。
【判断题】
真空接触器易出现电弧电流过零前就熄灭，出现截流现象，因而在电感电路中产生过电压。
【判断题】
接触器在电力机车上是用来频繁地接通或切断没有负载的主电路。
【判断题】
SS3型电力机车直流电磁接触器用在控制电路中。
【判断题】
接触器的辅助触头常用于接通和断开辅助电路，其额定电流为6～10A。
【判断题】
接触器在电力机车上是用来频繁地接通或切断没有负载的主电路。
【判断题】
CJ8Z．150Z型交流电磁接触器用于交流50 Hz，电压220 V的电路中操纵负载的接通或断开。
【判断题】
稳压二极管是二极管的一种，它在电路中的使用方法和普通二极管一样。
【判断题】
硅整流管上所标电压为反向不重复峰值电压。
【判断题】
硅整流管的额定电流，指的是它可通过的最大电流。
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— Fantastic! Nothing tastes ________.
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A. two-month B. two month’s C. two month D. two-months
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— Wow, _______! Will it pass our place?
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25. _______ are you going to the School Uniform Exhibition, Amy ?
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( ) 26. Where does the writer of "The little Prince" come from?
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( ) 27. What does the prince do after the fox tells him a secret?
A．He cares more about a flower and a sheep．
B．He meets many more strange adults on other planets．
C．He realizes his love for the rose and he goes back to his planet．
D．He discovers interesting things such as a snake, other roses and a fox
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( ) 28. What does "The little Prince" mainly talk about? It' s about _________．
A．the adult world B．the planet B -612
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( ) 29. What is the writer's main purpose（目的）in writing this passage？
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( ) 30. Why did the father not ask his son not to do this and do that？
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B．Because he was born from a poor family．
C．Because he was a man of few words．
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( ) 31. What would someone learn from this passage？
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C．What a good father should do． D．What the self-important is like．
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( ) 32. What may be the proper Chinese for the underlined part in the passage？
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( ) 33. Why did Natalie Smith pay for the six cars behind her?
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D. She wanted to show kindness.
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( ) 34. Judy Foreman copied down the phrase because she ___ .
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( ) 35. Who came up with the phrase according to the passage?
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( ) 36. What can we infer from the last paragraph?
A. People should practice random kindness to those in need.
B. People who receive kindness are likely to offer it to others.
C. People should practice random kindness to strangers they meet.
D. People who receive kindness are likely to pay it back to the giver.
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( ) 37.The greatest river for navigation is ___________.
A. the Nile B. the Amazon C. the Mekong D. the Mississippi
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( ) 38. From a dam, people can use the water for ___________.
A. keeping the rivers clean B. only making electricity
C. irrigation and making electricity D. washing clothes
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( ) 39. The water in the river is polluted because of _____________.
A. people's drinking water too much B. people's swimming in the river too much
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( ) 40. The best title of the passage is ___________.
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