选择题 34.  若有以下程序：
    #include＜iostream＞
    using namespace std;
    class Base
    {public:
      Base()
      {x=0;  }
      int x;};
    class Derived1:virtua1 public Base
    {public:
      Derived1()
    {x=10;}};
    class Derived2:virtuall public Base
    {public:
      Derived2()
      {x=20;}};
    class Derived: public Derivedl, protected Derived2{  };
    int main()
    {D erived obj;
      cout＜＜obj.x＜＜endl;
      return 0;}
    该程序运行后的输出结果是______。