overhead projector

例句：

1. 1.The teacher used the overhead projector to explain the math problem.
   老师使用投影仪来解释数学问题。
2. 2. The students gathered around the overhead projector to watch the presentation.
   学生们围在投影仪周围观看演示。
3. 3.The overhead projector was a useful tool for teaching large groups of people.
   投影仪是教授大群人的一个有用的工具。