Creative answers vs right/wrong answers

For every question we ask our students we need to have some idea of what kind of answer we're expecting.

• What's 2+2?

There is only one correct answer: 4.  If a stduent says 3 or 7 or yellow, they're wrong and must be corrected.

• What kinds of foods are healthy?

There are many right answers here, and the answers can even depend on outside factors such as culture, availability, or prior health condition.  For example, seafood can be healthy if you live near a clean coast and you know the fish is caught fresh.  However, pregnant women should avoid certain fish because they may contain too much mercury or might not have been cooked enough.
However, there are many wrong answers.  Coke isn't very healthy if you drink too much of it.  Therefore you'd need to plan very carefully what sort of answers are acceptable (for example, would you mark a student right or wrong for saying drinking 1 Coke a week is healthy?)

• What's your favourite food?

This is an opinion question.  As long as the student names a food (not, for example, a bicycle!), then they are "right".

• What do you think will happen next in the story?

This is a "right or wrong" question in the sense that once they continue the story they will find out if their prediction was correct, but it can't be judged that way.  It can only be judged as on the creativity and justification of the response.