单选题 有如下程序：
#include＜iostream＞
using namespace std;
class base{
public:
base(int x=0){cout＜＜x;}
};
class derived:public base{
public:
derived(int x=y){cout＜＜x;}
public:
base val;
};
int main(){
derived d(1);
return 0;
}
程序的输出结果是______。