AtlastfirefightershaveputoutabigforestfireinCalifornia．...

問題詳情：

At last firefighters have put out a big forest fire in California．Since then，they  41．  (set) about finding out 42．  the fire began．Forest fires are often caused by  43．  (break)glass or by cigarette ends which people carelessly throw away．Yesterday the  44．  (fireman)examined the ground but were not able to find any．They were also quite sure that a cigarette end didn’t start the fire．However，several hours passed  45．   a fireman accidentally discovered the cause．He noticed the remains of a snake which was wound(蜿蜒；纏繞)around the electric wires of a 16，000-volt power line．In this way，he was able to solve  46．  mystery．The  47．(explain) was simple but very 48． (usual)．A bird had snatched up the snake from the ground and then 49． (drop)it on to the wires．The snake then wound  50．  round the wires．When it did so，it sent sparks down to the ground and these immediately started a fire．

【回答】

41．have set

42．how

43．broken

44．firemen

45．before

46．the

47．explanation

48．unusual

49．dropped

50．itself

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