下面程序的运行结果是：（ ）#includeusing namespace std;class A{public:A(){cout<<"A";}};class B1:virtual public A{public:B1(){cout<<"B1";}};class B2:virtual public A{public:B2(){cout<<"B2";}};class C:public B1,public B2{public:C(){cout<<"C";}};int main(){C c;}