[originaltext] Lightning is a flow of electricity formed high above the eart

Lightning is a flow of electricity formed high above the earth.  A single flash of lightning 1.6 kilometers long has enough electricity to light one million light bulbs.
    The American scientist and statesman,  Benjamin Franklin, was the first to show the connection between electricity and lightning in 1752.  In the same year he also built the first lightning rod.  This device protects buildings from damage by lightning.     Modern science had discovered that one lightning contains over 15 million volts. A spark between a cloud and the earth may be as long as 13 kilometers, and travel at a speed of 30 million meters per second.
    Scientists estimate that there are about 2 000 million flashes of lightning per year.  Lightning hits the Empire State Building in New York 30 to 48 times a year.  In the United States alone it kills an average of one person every day.
    The safest place to be in case of an electrical storm is in a closed car.  Outside one should go to low ground and not under a tree.  Also, one should stay out of water and away from metal fences.  Inside a house, people should avoid opening doorways and windows and not touching wires or metal things.
29. What is the main idea of the passage?
30.How many people might be killed by lightning an average week according to the passage?
31.Which of the following is a safe place in an electrical storm?