This is a riddle I encountered recently and I can't solve it.
What goes in place of the question mark? No other info is given.
EDIT: Apparently there are a lot of possible answers, so I'll give some extra info on the context in which I found this riddle. I found it in a schoolbook for children of about 10 to 12 years old. It's a Flemish textbook, so all word related answers should be with Dutch words. However, since this riddle was in a chapter about patterns and lists, I'm inclined to go with Radhato's answer.