单项选择题

下面程序的运行结果为  # include <iostream.h>  class A  {    int num;  public:    A(inti){hum=i;}    A(A&a){num=a.num++;}    void print( ){cout << num;}  };  void main( )  {    Aa(1),b(a);    a.print( );    b.print( );  }

A.11
B.12
C.21
D.22