A Long, long ago people made fires from lightening ( 闪电 ). But they had to keep the fire burning, for they couldn't start it again if there was no lightening. Later, they found out hitting two pieces of stone together could make a spark ( 火花 ). The spark could fire dry leaves. In this way they could make the fire again if it went out. Then people also learned to make a fire by rubbing ( 摩擦 ). They made a hole in a piece of wood and put a smaller stick into the hole. They turned the stick again and again. After a few minutes they got a fire. Years went by, people learned other ways to make a fire. Sometimes they used the heat from the sun. They held a piece of glasses in the right way and made a piece of paper on fire. About two centuries ago, people began to make matches. Matches brought people a quick and easy way to make fires. Today matches are still being used, but people have more new ways to make fire. One of them is to use an electric fire starter. Of course an electric fir e starter is much more expensive than a box of matches. But it is very useful. 19. From the passage, we know that ________.