UDP属于（）层协议。
A.链路层
B.应用层
C.传输层
D.网络层
参考答案：C
关系规范化应遵循 ______ 原则。
The settlement is home to nearly l,000 people, many of ______ left their village homes for a better life
in the city. [ ]
A. whom
B. which
C. them
D. those
