若有以下程序：
#include ＜iostream＞
using namespace std;
class Base
public:
Base()
x=0;
int x;
;
class Derivedl: virtual public Base
public:
Derived1()
x=10;
;
class Derived2: virtual public Base publici
Derived2()
x=20;
;
class Derived :public Derived1,protected Derived2 ;
int main()
Derived obj;
cout＜＜obj.x＜＜end1;
return 0;
该程序运行后的输出结果是
A．20
B．30
C．10
D．0
