单选题 有如下程序：
#include ＜iostream＞
using namespace std;
class Base1
{
public:
Base1(int d) {cout＜＜d;}
～Base1(){}
};
class Base2
{
public:
Base2(int d) {cout＜＜d;}
～Base2(){}
};
class Derived:public Base1,Base2
{
public:
Derived(int a,int b,int c,int d):Base1(b),Base2(a),b1(d),b2(c){}
pnvate:
int b1:
int b2:
};
int main()
{
Derived d(1,2,3,4);
return 0;
}
执行这个程序的输出结果是______。