At the railway station，the mother waved goodbye to her daughter until the train was________.

A．out of sight

B．out of reach

C．out of order　　

D．out of place

关于乳、恒牙区别的说法，错误的是（）

A.乳磨牙体积依次减小

B.乳牙冠根分界明显

C.乳牙颈嵴明显突出

D.乳牙体积小，色乳白

E.乳牙根分叉大