若有以下程序: #include <iostream> using namespace std; class Basepublic: Base() x=0; int x; ; class Derived1: virtual public Basepublic: Derived1() x=10; ; class Derived2: virtual public Basepublic: Derived2() x=20; ; class Derived: public Derived1, protected Derived2 ; int main() Derived obj; cout<<obj.x<<end1; return 0;该程序运行后的输出结果是 【15】 。