In old times，man considered lightning to be one of the great mysteries（神秘事物）of nature．In fact a single flash of lightning 1.6 kilometers long has enough electricity to light one million lamps．
The American scientist，Benjamin Franklin，was the first to suggest that lightning is in fact electricity formed between the earth and clouds high above．It happened in 1752．In the same year，he also built the first lightning rod（避雷针）to protect buildings from being struck by lightnings．
Modern science has discovered that lightning is very strong and powerful．A lightning between a cloud and the earth may be as long as 13 kilometers，and travels at a speed of 30 million meters per second．Scientists have the opinion that there are about 2000 million flashes of lightning per year．In the United States alone，it kills almost one person per day．
The safest place to be in during an electrical（电的）storm is a closed car．Outside，one should go close to low ground for cover and not stop under a tree．Also one should stay out of water and away from metal fences．Inside a house people should keep away from open doorways and windows and not touch wires or metal things．
From this passage we know lightning is____．

A．one of the great mysteries of nature．

B．electricity high above the earth．

C．a kind of light．

D．the sound from the clouds．

In the U．S____．

A．every person can see lightning every day．

B．at least one person is killed by lightning every day．

C．there are about 6 million flashes of lightning per year．

D．about one person per day dies from lightning．

During a lightning storm，it would be best if you____．

A．stand under a tree．

B．go outside．

C．stay in a closed car．

D．stop near windows．

A lightning rod can______．

A．prevent accidents caused by lightning

B．stop lightning

C．protect buildings from being washed away．

D．delay the coming of lightning

A lightning between a cloud and the earth may be 13 kilometers long，and travels at
a speed of ______．

A．30 kilometres per second．

B．3000 kilometres per second

C．3 kilometres per second

D．30，000 kilometres per second