在关系模式R(姓名，性别，出生日期)中，最适合作为主键的是( )。
A．姓名
B．性别
C．出生日期
D．姓名、性别、出生日期
参考答案：D
When changing lanes, a driver should use his turning signal to let other drivers know .
A．he is entering which lane
B．which lane he is entering
C．is he entering which lane
D．which lane is he entering
脊椎动物有哪些主要特征？
