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问题 多项选择题

远端短路是指短路电流中交流分量不衰减的系统，下列情况（）可视为远端短路。

A.计算电抗标幺值X≥3

B.以供电电源容量为基准的短路电路时，认为电源母线电压维持不变，不考虑短路电流交流分量的衰减

C.电力系统电抗X与变压器低压侧电抗XTLV满足关系式XTLV≥2X

D.异步电动机反馈到短路点的电流超过不接电动机时该点的对称短路电流初始值的5%的短路

答案

参考答案：A, B, C

单项选择题

引起DIC的最常见的原因是：（）

A．感染

B．休克

C．创伤

D．肿瘤
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单项选择题

The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist.
Once the sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the earth, it will become a white dwarf star. The sun may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf.
After billions of years as a white dwarf, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the earth will be dark and cold. If any atmosphere remains there, it will have frozen onto the earth’s surface.

The word "there" underlined in Paragraph 4 refers to ______ .

A．our own planet

B．the outer surface of the sun
C．the core of a black dwarf

D．the planet mercury
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