Pollution is a common example of an externality that leads to market failure. 污染是外部性导致市场失效的一个常见的例子。
The most common example of a machine element is a gear, which, fundamentally, is a combination of the wheel and the lever to form a toothed wheel. 机械元件最常见的例子是齿轮,从根本上说,齿轮是轮子和杠杆的一种集合形成一个齿形的轮子。