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问题 单项选择题 A1/A2型题

运动神经传导速度测定中（）。

A.记录的是神经电位

B.记录的是复合性肌肉动作电位

C.根据一次刺激即可得出结论

D.需要平均叠加技术

E.有顺行法及逆行法两种检查方法

答案

参考答案：B

解析：运动神经传导速度测定是通过刺激神经，在肌腹上记录的复合性肌肉动作电位。其他答案都是感觉神经传导速度的测定。

单项选择题

西方国家中实行地方分权型单一制的国家的是( )

A．美国
B．澳大利亚
C．德国
D．日本
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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.

As a white dwarf, the sun will be ______ .

A．the same size as the planet Mercury
B．thousands of times smaller than it is today
C．around 35 million miles in diameter
D．cold and dark
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