以太

例句：

1. 1. The theory of relativity suggests that light travels at the speed of light.
   相对论理论表明光以光速传播。
2. 2. The speed of light is constant, regardless of the distance traveled.
   光速是恒定的，无论距离有多远。
3. 3. Light travels through a medium called light-speed.
   光通过一种叫做光速的介质传播。