Tornadoes  are one of the worst weather events on earth. Each year, tornadoes kill many people. The storms often carry homes, cars and trees from one place to another. And they can also _ anything when they pass by. A tornado comes from a thunderstorm  in the sky down to the ground. It is big at the top and small at the bottom. A tornado appears when winds in different directions meet in the cloud and begin to turn in circles. People can see tornadoes almost everywhere in the world. But most happen from late winter to middle summer. There is a second high season in November. During spring, warm air moves north and mixes with the cold air left from winter. In November, the opposite happens. Cold air moves south and mixes with the warm air left from summer. Tornadoes always come suddenly. Weather scientists have done something to predict  tornadoes. But the storms often move too fast for people to protect themselves. Last year, tornadoes killed more than one hundred people in United States. Scientists say the best place to be in is a small room, without windows, in the middle the lowest part of a building when tornadoes come. ,. From the passage, we know that   _  .
the United States has very few tornadoes tornadoes are one of the worst weather events in the world people should stay in big rooms with windows when tornadoes come more than one thousand people were killed by tornadoes in the USA last year