count digit set chain

例句：

1. 1. We need to count the number of people in the room.
   我们需要数一下房间里的人数。
2. 2. The teacher counted each student's homework carefully.
   老师仔细地数了每个学生的作业。
3. 3. Counting the stars above us gave me a sense of wonder.
   数天上的星星让我感到惊奇。