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