You have defined a class named Invoice that contains two non-static private fields, invoic...

You have defined a class named Invoice that contains two non-static private fields, invoiceNumber and amount. The class also contains a non-static public function that displays the amount; the function’s prototype is void showAmount();. When you write a main()function and declare one Invoice object named anInvoice, you can display the object’s amount field with the statement ___________.

a. cout << Invoice::showAmount();

b. cout << Invoice.showAmount();

c. cout << anInvoice.showAmount();

d. None of the above