一打鸡蛋的价格是1.99美元。

A dozen eggs cost $1.99.

我买了一打鸡蛋。

I bought a dozen eggs.

当你买鸡蛋时，你会买一打鸡蛋。

When you buy your eggs, you buy a dozen eggs.

我买了一打鸡蛋。

I bought a dozen eggs.

她买了一打鸡蛋。

She bought a dozen eggs.

如果你不能让出一打鸡蛋，半打也行。

If you can't spare a dozen eggs, half a dozen will do.

但是10就像1、一打鸡蛋或一颗鸡蛋一样，是一个单位。

But 10, just like one, just like a dozen eggs, just like an egg, 10 is a unit.