下列器具中去除颈部和根面上的菌斑最有效的是
A．牙线
B．牙签
C．牙间刷
D．橡胶按摩器
E．以上器具效果相近
参考答案：C
We are not sure which restaurant_______tonight.
A．eating at
B．for eating
C．to eat at
D．we eat
计算题：已知一管材的延伸系数为15.60，其变形程度δ%为多少？
