Event Vs Recursion - Program That Has A Large Set Of Classes In It - Each Class Will Need To Add One Or More Strings To One Of Two Lists

I have a program that has a large set of classes in it. A certain incident (I won't call it an event, yet, as that has a specific meaning that will cause trouble later) needs to a relatively small subset of these classes a question. The subset of classes will need to respond to the question, but for it to be able to do so, the classes may first need to ask a similar question of the same subset, which may prompt yet a further question, though this recursion will never go more than three or four levels down. Since only a small subset of these classes will participate in the questions, while the majority will never participate, and since all of these classes are virtually identical, and I can know at design time whether any given class is part of the subset or not, an event is appropriate. The main class can raise an event, and those classes in the subset can handle the event, while those classes that are not in the subset won't handle the event. Furthermore, any of these classes can raise the event again with different parameters, as needed. Thus far, an event appears to be ideal.

The problem is this: As a result of the event, each class will need to add one or more strings to one of two lists. Event handlers can't return anything, so I can't be using the return values from functions to populate these lists.

Two options appear possible:

1) Include the two lists in the event arguments.

2) Have the two lists be accessible to all classes, and don't pass anything around.

The second part of the problem is that the event is effectively a question being asked of each class, and no action can be taken until each class has responded. If I simply raise an event and let each class respond, can I be certain that all classes that should respond have? An alternative solution would be to have each class expose a method, and call these methods for each class in turn. By doing this, I could get return values, but I would have to call the methods for ALL the classes, not just the subset that actually cares (the classes are all different types, but they all implement a common interface, and are added to a List (of ) that interface, so I can iterate through them all without much difficulty). So, the event seems more efficient, but adding a function to the common interface for the classes is the approach most certain of being a solution.