Thunder is generated by the tremendous heat released in a lightning discharge. Temperatures near the discharge can reach as high as 50,000F within thousandths of a second. This sudden heating acts as an explosion, generating shock waves we hear as thunder.
About 2,000 thunderstorms are occurring in the world at any time, generating about 100 light
ing strikes every second, or 8 million daily. Within the United States, lightning strikes are estimated at 20 million a year, or about 22,000 per day. You have a 1-in-600,000 chance of bring struck by lightning during your lifetime. Lightning can strike twice or more in the same spot. The Empire State Building in New York is struck by lightning about two dozen times annually.
You can measure how far you are from a lightning strike by counting the seconds between viewing the flash and hearing the bang, and then dividing by five. This approximates the mileage.
练习:1-4题的要求是,从第一个方框的六个选项A、B、C、D、E、F中选出四个选项为注明的段落各配一个合适的小标题。5-8题的要求是,从第二个方框的六个选项A、B、C、D、E、F中选出四个选项完成每个句子。
1. Paragraphs 2 and 3
2. Paragraph 4
3. Paragraph 5
4. Paragraph 6
A Cloud-to-ground lightning occurring in the U.S.
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