单选题 在下面程序中，A、B、C、D四句编译时不会出错的是( )。 #include ＜iostream＞ using namespace std; class Base{ public: Base(); Base(int e):count(C) {} virtual void print() const = 0; private: int count; }; class Derived :public Base{ public: Derived():Base(0) {} Derived(int C) :Base(C) {} void printt() const{cout＜＜ "Derived"＜＜endl:} }; void main( ) { Derived d(10); Base *pb; pb = &d; //A Base &cb= d; Derived dd = *pb; //B Derived &cd = cb; //C Base bb = d; //D