Tonight we're _____ to a thirteen year old boy.[ ]
A. telling
B. saying
C. talking
答案:C
一般说来,使用四环素不致引起牙着色的年龄为()。
A.1~2岁以后
B.2~3岁以后
C.3~4岁以后
D.4~5岁以后
E.6~7岁以后