Without the use of colour for closed-circuit work there would not be such excellent demonstrations of operations and classroom instruction in medical schools and monitoring of certain industrial processes in factories as we have today.

• 闭路电视没有颜色的使用，我们现在就不会有精彩的操作示范和医学院里课堂训练以及在工厂里某些工业生产过程的监控。