In the Observer pattern's pull model variation, a ConcreteObserver class must 10 points O determine what to aggregate define an updating interface O ascertain what was changed maintain a relationship to the abstract Observer In the Observer pattern's "push model" variation, the Subject class* O uses a generic interface for registration. O updates observers regardless of what has changed in the subject's state. 10 points implements the calls to the observer's update method in the derived ConcreteSubject. O has specific knowledge about the observer interface. Why would a software designer modify the Observer10 points Update method to take a reference to a Subject asa parameter? (ex: Observer:Update(Subject&)) * To allow Observers to know which of multiple ConcreteSubject objects was updated. To allow Subjects flexibility on which Observer objects should be notified None of the above. This is a violation of Liskov Substitution Principle. None of the above. This modification would be called the GoF Mediator pattern O