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