zero insertion and deletion

例句：

1. 1. The zero sum game means that the total amount of money cannot be increased or decreased.
   零和游戏意味着总金额不能增加或减少。
2. 2. In mathematics, a zero is used to represent an empty space or a missing value.
   在数学中，零用来表示一个空的空间或缺失的值。
3. 3. The company's revenue has been zero for the past six months.
   这家公司过去六个月的营业额为零。