下面代码执行后的输出结果为（ ）
#include <iostream>
using namespace std;
class Animal {
public:
void eat() {
cout<<"1"<<endl; }
virtual void drink() {
cout<<"2"<<endl; }
};
class Dog: public Animal {
public:
void eat() {
cout<<"3"<<endl; }
void drink() {
cout<<"4"<<endl; }
};
int main(void) {
Animal ani;
Dog dog;
Animal *p = &ani;
p->eat(); p->drink();
p = &dog; p->eat(); p->drink();
Animal *ptr = (Animal *)&dog; ptr->eat();
ptr->drink();
return 0; }