单选题 有如下程序：
#include＜iostream＞
using namespace std;
Class Base
{
protected:
int id;
public:
Base(){id=1;}
};
class Middle1:virtual public Base
{
public:
Middle1()(id+=1; cout＜＜id;}
};
class Middle2:virtual public Base
{
public:
Middle2(){id+=2; cout＜＜id;}
};
class Derived:public Middle1, public Middle2
{
public:
Derived(){cout＜＜id＜＜endl;}
};
int main()
{
Derived obj;
return 0;
}
其运行结果是______。