Given the following class hierarchy in which each class defines a public default construct...

Given the following class hierarchy in which each class defines a public default constructor and virtual destructor:

class A { /* .. . */};class B : public A { /* ... */};class C : public B { /* ... */};class D : public B, public A { /* ... */};

which, if any, of the following dynamic_casts fail?

(a) A *pa = new C;

B *pb = dynamic_cast< B* >(pa);

(b) B *pb = new B;

C *pc = dynamic_cast< C* >(pb);

(c) A *pa = new D;

B *pb = dynamic_cast< B* >(pa);