Useful for demonstrating the different tenses.
An English teacher spent a lot of time marking grammatical errors in her students' written work. She wasn't sure how much impact she was having until one overly busy day when she sat at her desk rubbing her temples a student asked, "What's the matter, Mrs. Sheridan?"
"Tense," she replied, describing her emotional state.
After a slight pause the student tried again, "What was the matter? What will be the matter? What has been the matter? What might have been the matter... ?"