第一恒磨牙萌出特点是A．萌出较早，患龋率低B．牙龈位置稳定不发生改变C．牙釉质牙本质钙化度高，耐酸

Have you ever seen a ______ bag on the table？

A．plastic small black

B．black small plastic

C．plastic black small

D．small black plastic

He pointed at the new car and asked, "___ is it？ Have you ever seen it before？"

A.Why

B.Where

C.Who

D.Whose

Have you ever seen a__________bag on the table？

A.plastic small black

B.black small plastic

C.plastic black small

D.small black plastic

Have you ever seen a ______ bag on the table？

A．plastic small black

B．black small plastic

C．plastic black small

D．small black plastic

A．a tree

B．such tree

C．an tree

D．tree

A、have ever seen

B、has ever seen

C、ever has seen

D、had ever seen

--Have your students ever seen the silent film？

--No, they are too young ______ the old film.

A. to seeing

B. have seen

C.to have seen

D. to have