单项选择题

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

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