验钞机是利用荧光物质在 线的照射下能够发光的原理制成的；家中的电视遥控器是靠 线来实现对电视机的控制的。
紫外 红外
I soon found that the work I was doing had already been done by someone else－ , I was wasting my time.
A．what’s worse
B．all in all
C．all the best
D．in other words
一台焊机只有一条外特性曲线。( )
