c中的多态性,父类向量中的类型丢失

class A {};
class B : public A {};
class C : public A {};


class X
{
    void foo(A) { std:: cout << "A"; }
};

class Y : public X
{
    void foo(B) {std::cout << "B"; }
};

class Z : public X
{
    void foo(C) {std<<cout <<"C"; }
};

int main()
{
    B b;
    C c;

    Y y;
    Z z;

    y.foo(b);//prints B // b is a B,and Y::foo takes a B,hence print B
    y.foo(c);//prints A // mismatch between types,fall BACk and print a
    z.foo(b);//prints A // mismatch between types,fall BACk and print a
    z.foo(c);//prints C // c is a C,and Y::foo takes a C,hence print C

    std::vector<A> v;
    v.push_BACk(b);
    v.push_BACk(c);

    //In this loop,it always prints A,but *this is what I want to change* 
    for (size_t i = 0; i < v.size(); ++i)
    {
        z.foo(v.at(i));
        y.foo(v.at(i));
    }
}

是否有可能使项目打印出与硬编码调用相同的结果？
这意味着我会将它们视为原始类型,而不是其父类型？
或者,一旦我把它们放在A的矢量中,它们将永远属于A型？