anulación de unidad
Protected - can only be called from inside its class,
OR within a subclass which implements that class
Virtual - a method which may be overridden by a subclass,
but still contains an implementation. An overriding
member in a subclass may also call base.MethodName()
to invoke the underlying Virtual method before/after
doing its own thing
Override - You write this when you are overwriting a virtual class that
comes from the parent.
Jesús Angarita