5、Al Ossinger，an experienced mountain guide，knew it was time to leave Longs Peak in Colorado’s Rocky Mountain National Park，and get off‘quickly．The sky had turned threatening dark，and his ice ax at times gave out upset sounds．Suddenly，as Ossinger was  crossing a large mass of rock，both hands pressed against it for balance，there was a roar，a flash of light and an electric current charged through his arms．

“In that second. I thought 1 was finished，”he said，“Then I realized 1 was still there―the jolt(震動(dòng))hadn’t knocked me off．My body and legs were all right，but my arms  were paralyzed from the shoulder down．’’Fortunately Ossinger was able to continue down and soon the feeling began to return to his shoulders，upper arms，and，two hours later，his fingertips．Ossinger was a lucky man．

A single stroke of lightning，which is usually three to four miles long，travels at speeds of up to 100，000 miles per second．In a single flash，it can carry 100 million volts of electricity and reach a temperature of 55，000 degrees Fahrenheit，five times hotter than the surface of the sun．During its brief life span，lightning carries enough energy to power  a 100-watt light bulb for as long as three months．If you find yourself unlucky enough to be  near lightning’s path，you could suffer a direct hit，sending electrical current though your body for some 5 00 milli-seconds．Because of the short duration，severe burns aren’t common and the resulting burns are usually superficial(表面的)．

According to the national Weather Service，more people have been killed by lightning in the United States during the past 30 years，an average of 87 a year-than by either tornadoes or hurricanes，484 people were injured in 1994 alone．These“swords from the sky” are also responsible for an estimated$100 million to$300 million of property damage a year．During the 1980s an average of 5502 wildfires a year were sparked by lightning on national forest lands alone．

Earth is struck by at 1east 100 of these flashes every second-more than 8．6 million strikes a day．For all its destructive power，lightning has its good sides too．It’s likely that humans discovered fire from some early lightning-sparked flames．And all that activity above the earth may help create ozone(臭氧)，which protects us from the sun’s harmful rays．Lightning dancing across a summer night sky is a force to be respected and appreciated-from a distance．

 

68．Electrical lightning is called“swords from the sky”to mean_________．

A．it looks 1ike swords                                    B．it can kill people

C．it is sent by God                                         D．it comes naturally

69．When Ossinger felt some electrical current charged through his arms，_________．

A．he thought it was going to rain                     B．he dared not move about any more

C．he tried to move further up                          D．he thought his arms wouldn’t move

70．According to the passage we can say that____________________.

A．people caught by lightning may go disabled at once

B．1ightning strikes may do harms to human beings

C．more forest fires will be caused by lightning

D．1ightning is a rich energy resource to humans

71．In the passage the author implies that__________．

A．we all should try to avoid all thunderstorms

B．we should make full use of the lightening

C．we should recognize the positive effects of lightning

D．we should learn about the lightning as much as possible