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 Derivedl : virtual public Base

public:
Derivedl()

x=10;

;
class Derived2 : virtual public Base

public:
Derived2()

x=20;

;
class Derived : public Derivedl,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