Brighton is a popular seaside town on the south coast of England. Not long ago, some policemen were very_____（21）. There had been several serious accidents_____（22）by motorists driving too fast. The police started to set up a speed trap（速度监视器）. They measured_____（23）of 88 yards on a straight road and watched to see_____（24）a car took to 25 that far. They knew that if a car took six seconds, it was traveling faster_____（26）the_____（27）limit of 30 miles an hour.
When the policemen were ready, they hid_____（28）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_____（29）of each car and the name and address of the driver. But for the next half an hour the policemen didn't see anybody_____（30）too fast. They thought that this was very_____（31）. One of the them drove a quarter of a mile along the road and saw two students_____（32）on the grass. They were holding up a sheet of cupboard so that motorists could see it. On the notice one of the students _____（33）: "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_____（34）to stop the police catching motorists who were_____（35）the law.
33_____
A、writes
B、was writing
C、written
D、had written
【正确答案】：D
【题目解析】：谓语动词题。此处意为：一个学生在牌子上写着。根据文中前后的时态，可排除A和C。D项为过去完成时，符合题意。
