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脉宽调制型（PWM）逆变器是随着、高开关频率的新型电力电子器件的产生，而逐步发展起来的，对其主要优点描述正确的是（）。A.
主电路有多个可控的功率环节，开关元件多，结构复杂
B.
使用不可控整流器，使电网功率因数与逆变器输出电压的大小无关而大于1
C.
逆变器本身同时完成调频和调压的任务
D.
调节过程与中间滤波环节的滤波元件无关，变频器动态响应加快
E.
可获得比常规阶梯波更好的输出电压波形，输出电压的谐波分量极大地减少，能抑制或消除低次谐波，实现近似正弦波的输出交流电压波形
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【简答题】万能转换开关是由 叠装而成、控制多回路的主令电器。
【单选题】Typical drawings in machine manufacturing are classified as assembly drawings and __________.
A.
part drawings
B.
basic view
C.
axonometric drawing
D.
sketch
【单选题】Which of the figures below the line of drawings best completes the series?
A.
B.
C.
D.
【单选题】Human' s Hands Archaeological records--paintings, drawings, and drawings of humans engaged in activities involving the use of hands--indicate that humans have been predominantly right - handed for mor...
A.
Human ancestors became predominantly right- handed when they began to use tools.
B.
It is difficult to interpret the significance of anthropological evidence concerning tool use.
C.
Human and their ancestors have been predominantly right - handed for over a million years.
D.
Human ancestors were more skilled at using both hands than modern humans.
【单选题】患儿,女,3 岁。经常咳嗽,每年冬天患肺炎。查体 面色苍白,胸骨左缘第3、4肋间闻及3 6 级收缩期喷射样杂音,肺动脉瓣区第二心音亢进。诊断为,室间隔缺损。针对该诊断应采取的主要护理措施是
A.
严格卧床休息
B.
调整饮食
C.
动静适度
D.
补充足够液体
E.
注意预防感染
【单选题】According to the passage, what is noteworthy about Crumb's drawings?
A.
His drawings are less expensive than other comic books.
B.
He put his own experience into the drawings.
C.
His drawings could attract the viewers' attention.
D.
His drawings are in black and white.
【简答题】I make designs, drawings or pictures that are used especially in the production of book. I am a ____________.
【单选题】Why did the little prince langh when he saw "my" drawings?
A.
Because "my" drawings were true to life.
B.
Because "my" drawings were just not true to life.
C.
Because "my" drawings reminded him of some good memories.
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