The phenomenon of lightning has been a source of danger and mystery through the centuries, and only recently have scientists begun to understand its true nature. We know now that lightning is a huge electrical spark caused by the interaction of electrically charged particles in the atmosphere. During a thunderstorm, heavy particles take on a negative charge and fall to the bottom of clouds, while particles holding a positive charge rise to the top. Lightning results when energy flows between the two types of charges.

　　What is still not understood is the process by which particles become electrically charged. Most scientists believe that a cloud’s light ,rising moisture and tiny pieces of ice collide with hail and other heavy, falling particles. The collision may cause these elements to take on either a positive or negative charge.

　　The most feared form of lightning is that which strikes the ground in one or more electrical discharges called strokes. Any one of these strokes is capable of causing death , destroying property ,or igniting fires. It is interesting to note that the bright flash of light produced by a stroke actually occurs as the discharge returns to the sky and not as it descends towards the ground. This return stroke heats surrounding air and causes it to expand, thus producing a wave of pressure called thunder.

　　1.Which of the following is the best title for the passage?

　　A. A Dangerous Phenomena

　　B. Atmospheric Occurrences

　　C. The Nature of Lightning

　　D. Scientific Mysteries

　　答案C。依據(jù)全文：文章開始談到多少世紀(jì)以來，閃電給人來帶來危險(xiǎn)，同時(shí)一也是一種神秘的自然現(xiàn)象，而且直到最近，科學(xué)家們才開始弄清楚閃電的真正本質(zhì)，接下來文章講述了閃電的形成，粒子帶電的過程以及最可怕的一種形式即閃擊的形成。故答案為C。

　　2.The passage states that lightning is ________.

　　A. a recent source of mystery

　　B. a giant spark of electricity

　　C. an electrically charged particle

　　D. a type of thunderstorm

　　答案B。依據(jù)文章第一段的第二句：我們現(xiàn)在知道閃電是一種巨大的電火花，它是由大氣層中帶電的粒子相互作用形成的。故答案為B。

　　3. According to the passage, lightning results from ________.

　　A. a flow of energy between positive and negative charges

　　B. discharges in a heavy, thunderstorm

　　C. the rising and falling of heavy particles

　　D. great amounts of electricity in the atmosphere

　　答案A。依據(jù)文章第一段的第二句至第一段結(jié)尾：我們現(xiàn)在知道閃電是一種巨大的電火花，它是由大氣層中帶電的粒子相互作用形成的，雷雨發(fā)生時(shí)，大氣中重的顆粒帶有負(fù)電荷并降落到云層的底部，而帶有正電荷的顆粒升到高空，當(dāng)能量在兩種電荷中流動(dòng)的時(shí)候，閃電就發(fā)生了。故答案為A。

　　4. According to the passage, particles become electrically charged when ________.

　　A. light ,ascending matter collides with heavy, falling elements

　　B. energy flows between light and heavy charged particles

　　C. heavy particles rise to the tops of clouds

　　D. a return stroke heats the surrounding air and causes it to expand

　　答案A。依據(jù)文章第二段第二句話至第二段結(jié)尾：人們還沒有搞清楚的是通過什么樣的過程粒子成為帶電荷的粒子，但大多數(shù)科學(xué)家們認(rèn)為，云中上升的重量輕的水分和微小的冰粒會(huì)與下降的雹子或其它分量重的粒子發(fā)生碰撞。這樣的碰撞可能會(huì)使得這些粒子帶上正電荷或負(fù)電荷。故答案為A。

　　5. The author implies that most people believe they observe lightning_______.

　　A. as being slower than the speed of light

　　B. only in conjunction with the sound of thunder

　　C. as it rushes down to strike the earth

　　D. in the form of strokes released in the atmosphere

　　答案C。依據(jù)文章最后一段第三句：人們會(huì)饒有興趣地注意到，由閃擊造成的閃電實(shí)際上是在放電返回空中而不是在它向地面降落的時(shí)候發(fā)生的。故答案為C。

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