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  3. The Northern Lights The sun is stormy and has its own kind of weather. It is so hot and active that even the Sun’ s gravity

The Northern Lights The sun is stormy and has its own kind of weather. It is so hot and active that even the Sun’ s gravity

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问题                         The Northern Lights
    The sun is stormy and has its own kind of weather. It is so hot and active that even the Sun’ s gravity cannot hold its atmosphere in check! Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma(等离子体), and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun, the stronger the solar wind.
    The solar wind constantly streams toward the Earth, but don’ t worry because a protective magnetic field surrounds our planet. The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles. The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth’ s magnetic field, the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.
    The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons(电子)trapped in the belts to fall into the Earth’ s atmosphere at the poles. As the electrons fall into the Earth, they collide with gas molecules in the atmosphere, creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen(氮)glow red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky, they create the Northern Lights and the Southern Lights.
    Watching auroras(极光)is fun and exciting, but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate, flicker, or even move like waves. During solar maximum, auroras are seen as far south as Florida, even Mexico!
    Auroras often seem to be very close to the ground, but the lowest aurora is still about 100 kilometers above the ground, a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long, a few hundred kilometers high, but only a few hundred meters thick.
    We hope you are able to travel to far-north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!
The Sun’ s gravity is too weak to keep its plasma from flowing to the Earth.
选项 A、真
B、假
C、Not Given
答案B
解析 利用题干句中的特征词Sun’s gravity及plasma共同作为线索，在文章第一段中找到相关信息。第二句意为太阳表面高温、多风，气候变化异常活跃，这使得太阳的引力无法控制住其大气层。第三句意为能量以带电粒子流的形式高速远离太阳表面。第四句说这种被称为等离子体的粒子流就是来自太阳的太阳风暴。可见造成太阳不能阻止其大气层中的等离子体流向地球的主要原因并不是太阳引力弱的问题，而是由于太阳过于活跃、太热所致。
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