Suppose that p1 and p2 are both pointers to the same dynamically-allocated integer value; y is a local integer variable. After the execution of which of the statements below is the pointer variable p1 considered a dangling pointer (not pointing to a valid memory address)?

a. p1 = p2;

b. p1 = 0;

c. p2 = 0;

d. p1 = &y;

e. delete p2;

f. p2 = &y;