First listen and then answer the question.
What caused the fire?
At last firemen have put out a big forest fire in California. Since then, they have been trying to find out how the fire began. Forest fires are often caused by broken glass or by cigarette ends which people carelessly throw away. Yesterday the firemen examined the ground carefully, but were not able to find any broken glass. They were also quite sure that a cigarette end did not start the fire. This morning, however, a firemen accidentally discovered the cause. He noticed the remains of a snake which was wound round the electric wires of a 16，000-volt power line. In this way, he was able to solve the mystery. The explanation was simple but very unusual. A bird had snatched up the snake from the ground and then dropped it on to the wires. The snake then wound itself round the wires. When it did so, it sent sparks down to the ground and these immediately started a fire.
New words and expressions 生词和短语
fireman(1.1)/’faiəmən/ n. 消防队员
Notes on the text 课文注释
1 at last，最后，终于。
2 they have been trying to find out how the fire began，他们一直试图找出起火的原因。句中短语动词 find out 的宾语是一个从句 how the fire began。
3 broken glass，碎玻璃。
4 cigarette ends，烟头。
5 in this way，就这样。