关于属性的使用正确的是

A、private int num; public string Num { get{return num;} set{num=value;} }
B、private int num; public int Num { get{return num;} set{num=value;} }
C、private int num; public int Num { get{num=value;} set{return num;} }
D、private int num; private int Num { get{return num;} set{num=value;} }