下列代码中， d1->work(); 和 d2->work(); 输出不同结果的主要原因是

class Device{
public:
    virtual void work(){
        cout<<"Device is working"<< endl;
    }
    virtual~Device(){}
};

class Printer: public Device{
public:
    void work() override{
        cout<<"Printer is printing"<< endl;
    }
};

class Scanner: public Device{
public:
    void work() override{
        cout<<"Scanner is scanning"<< endl;
    }
};

int main(){
    Device* d1= new Printer();
    Device* d2= new Scanner();
    d1->work();
    d2->work();
    delete d1;
    delete d2;
    return 0;
}