氟牙症多见于恒牙，乳牙者甚少，是因为（）
A.胎盘屏障
B.8岁以后生活在高氟区
C.刷牙时吞服含氟牙膏
D.氟骨症的表现
E.以上都不对
参考答案：A
Tom likes _____ to the movies with his friends on weekends. [ ]
A. to going
B. goes
C. going
D. go
The bear looked ________the room, but there was no one in it.
A．at
B．into
C．for
D．about
