可被刮除的黄棕色斑（）
A．脱矿性斑
B．色素附着
C．四环素牙
D．釉质钙化不全
E．氟牙症
参考答案：B
Many of my students, __________ Zhang Hua and Li Yong, are working very hard, and we should learn from them.
A．for example
B．such as
C．that is
D．as well
