--I wonder how you have improved your spoken English so fast, Li Lei.

--          Chatting with my foreign friend.He’s been here for some time,you know.

A．On

B．With

C．In

D．By

用二维表数据来表示实体及实体之间联系的数据模型为( )。

A) 层次模型
B) 网状模型
C) 关系模型
D) E-R模型