There is no power like _____ power of confidence, and there is no student as competitive as ______

student who trusts his own abilities. [ ]

A . the; a          

B. a; the            

C. /; a          

D. the; /

目前使用最多的是（）数据库。

A、网络型

B.关系型

C.层次型

D.混合型