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