There         a lot of farmland here. But now you can only see tall buildings.

A．used to have

B．is used to being

C．used to having

D．used to be

在Visual FoxPro中，在数据库中创建表的CREATE TABLE命令中定义主索引、实现实体完整性规则的短语是( )。

A．FOREIGN KEY

B．DEFALT

C．PRIMARY KEY

D．CHECK