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
A．20
B．30
C．10
D．0
