Consider the class A { public: virtual void isamA() { cout < < "base "; } }; a. Derive two classes from class base, and for each define isamA() to write out the name of the class. b. Declare objects of each class, and call isamA() from them. c. Assign the address of objects of the derived classes to base pointers and call isamA() through the pointers. d. Remove the virtual keyword from the base class member function, run your code again, and compare the results.