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．
【小题1】From this passage we know lightning is____．

An old farmer lived with his grandson. Each morning, the   16  got up early and read his Bhagavad Gita(薄迦梵歌).
One day the grandson asked, “Grandpa! I try to read the book like you   17  I can’t understand it, and I forget it easily. What’s the   18  of reading it?”
The grandfather said, “Take this coal(煤炭) basket down to the   19  and bring me back a basket of water.”
The boy did as his grandfather   20  ,but all the water ran   21  he got home. The grandfather laughed, “You’ll have to move faster next time.”
This time the boy   22  faster, but again the basket was empty. He told his grandfather that is was   23  to carry water in a basket. He wanted to use a bottle instead, but the old man said, “I just want a basket of water. You’re not   24  hard enough.”
The boy wanted to show his grandfather that the water would surely run. He again put the   25  into the river and ran hard. But there wasn’t anything in it again. He said   26  ,“Look, grandpa, it’s useless!”
“Watch the basket.” said the grandfather.
For the first time the boy   27  the basket was different. It had changed from a dirty old coal basket into a   28  one, inside and out.
“Boy, you might not understand or remember   29  when you read the book, but when you read it, you will be   30  ,inside and out. That’s what you got from it.”