A:18,1
B:8,2
C:18,3
D:18,8
— That's a good habit.
- Excuse me. Do you know __________?
- Well, go along this street and turn right. There’s one on the left.
9+____=11 9+____=17 9+____=13
11-9=____ 17-9=____ 13-9=____
下列各项属于同一个结构层次的是( )