asterisk with based variables

例句：

1. 1. The teacher drew an asterisk on the board to emphasize the point.
   老师在黑板上画了一个星号来强调这一点。
2. 2. The student wrote "A" for "Apple" and crossed out the asterisk to show he didn't understand.
   学生写了“A”代表“苹果”，并划掉了星号表示他没有理解。
3. 3. In math, we use asterisks to indicate that a number is not included in acalculation.
   在数学中，我们使用星号来表示一个数不包含在计算中。