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     Brighton is a popular seaside town on the south coast of England. Not long ago, some policemen were very . There had been several serious accidents  by motorists driving too fast. The police started to set up a speed trap (速度监视器). They measured  of 88 yards on a straight road and watched to see  a car took to  that far. They knew that if a car took six seconds, it was traveling faster  the  limit of 30 miles an hour. 

     When the policemen were ready, they hid  a hedge (树篱) and started to time passing cars. During their first half an hour, they caught five drivers. The policemen wrote down the  of each car and the name and address of the driver. But for the next half an hour the policemen didn’t see anybody  too fast. They thought that this was very . One of them drove a quarter of a mile along the road and saw two students  on the grass. They were holding up a sheet of cupboard so that motorists could see it. On the notice one of the students :"Danger. Speed trap." 

     The policemen took the notice away and wrote down the names of the students. Later on they were each fined £5 for  to stop the police catching motorists who were  the law.