spur-mark

例句：

1. 1. The car's horn is a useful marker for signaling the driver to slow down.
   汽车的喇叭是提醒司机减速的一个有用的标志。
2. 2. The teacher's praise was a powerful spur to her students' improvement.
   老师的表扬是激励学生们进步的一个强有力的动力。
3. 3. The new policy has been credited with providing an impetus for economic growth.
   新政策被认为是促进经济增长的一个动力。