I know the name of the pretty girl on the playground, but I am not sure        .     [ ]

A. how old is she      

B. where she lives     

C. where does she come from      

D. how tall is she

在一定时间里，某人群新发生龋病的频率（）

A.DMFT

B.龋均

C.患龋率

D.龋病发病率

E.根龋指数