若有以下程序：
# include ＜iostream＞
using namespace std;
class Basepublic:
Base ( )
x=0;
int x;
;
class Derived1 : virtual public Basepublic:
Derived1 ( )
x=10;
;
class Derived2 : virtual public Basepublic:
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．10
B．20
C．30
D．0