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=0) cout＜＜x;
private:
Base val;
;
int main()
Derived d(1);
return 0;

程序的输出结果是( )。

A．0
B．1
C．01
D．001