—I’d like to make an appointment with Doctor Smith．Would 9:00 tomorrow be all right?

—     ．Her schedule is full in the morning.

A．Yes, she’s free then

B．I’m afraid not

C．You must be joking

D．Wel1, it depends

常见的数据模型有3种，它们是______。

A．网状、关系和语义

B．层次、关系和网状

C．环状、层次和关系

D．字段名、字段类型和记录