A dozen means twelve.
一打，就是十二个。
But why twelve, not ten?
可为什么是十二，不是十呢？
Long ago, people counted with their thumb.
很久以前，人们用大拇指来数数。
One hand has twelve parts to count.
一只手正好有十二个可以数的指节。
That is why a dozen is twelve.
这就是“一打”等于十二的原因。
Eggs are often sold by the dozen.
鸡蛋常常一打一打地卖。
