题目内容：
请回答题Questions 11 to 15 are based on the following passage:
Fire can help people in many ways. But it can be very dangerous. Fire can heat water, warm houses, give light and cook. But fire can bum things, too. It can bum trees, houses, animals or people. Sometimes big fires can bum forests.
Nobody knows for sure how people began to use fire. But there are many interesting stories about the first time a man or a woman started a fire. One story from Australia tells about a man very, very long time ago. He went up to the sun by a rope (绳子) and brought fire down.
Today people know how to make a fire with matches (火柴) . Children sometimes like toplay with them. But matches can be very dangerous. One match can bum a piece of paper and then it might burn a house. A small fire can become a big fire very fast. Fire kills many people every year. So you must be careful with matches. You should also learn to put out fires. (80) Fires need oxygen(氧气). Without oxygen they will die. Cover a fire with water, sand, or sometimes with your coat. This keeps the air away from a fire and kills it. Be careful with fire, and it will helpyou. Be careless with fire, and it will burn you.
How did people begin to use fire? A．Not everybody knows how people began to use fire.
B．Nobody knows how to make a fire.
C．It is an Australian who started a fire.
D．We are not sure how people began to use fire.
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