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

Best Answer:C

详解：答案C。依据全文：文章开始谈到多少世纪至今，闪电给人来带来危险，同时一也是一种神秘的自然现象，而且直到近期，科学家们才开始弄清楚闪电的真正本质，接下来文章讲述了闪电的形成，粒子带电的过程以及最可怕的一种形式即闪击的形成。故答案为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

Best Answer:B

详解：答案B。依据文章第一段的第二句：我们目前知道闪电是一种巨大的电火花，它是由大气层中带电的粒子相互作用形成的。故答案为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

Best Answer:A

详解：答案A。依据文章第一段的第二句至第一段结尾：我们目前知道闪电是一种巨大的电火花，它是由大气层中带电的粒子相互作用形成的，雷雨发生时，大气中重的颗粒带有负电荷并降落到云层的底部，而带有正电荷的颗粒升到高空，当能量在两种电荷中流动的时候，闪电就发生了。故答案为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

Best Answer:A

详解：答案A。依据文章第二段第二句话至第二段结尾：人们还没有搞清楚的是通过什么样的过程粒子成为带电荷的粒子，但大多数科学家们觉得，云中上升的重量轻的水分和小小的冰粒会与下降的雹子或其它分量重的粒子发生碰撞。这么的碰撞可能会使得那些粒子带上正电荷或负电荷。故答案为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

Best Answer:C

详解：答案C。依据文章最后一段第三句：人们会饶有兴趣地注意到，由闪击导致的闪电实际上是在放电返回空中而不是在它向地面降落的时候发生的。故答案为C。