Which of the following is not true about a set of methods that are usefully polymorphic? This question only considers inheritance-based polymorphism i.e. it does not consider Interfaces. Select one: a. They must have identical signatures and therefore belong to separate classes b. Their classes share a common ancestor class from which they are ultimately inherited c. Each should produce a specialised effect appropriate to their class and therefore different to each other d. To be invoked polymorphically, an object of their class's type must be referenced by a variable of an ancestor's type common to all of them e. If you think all of the above are true, select this option