When your teacher is ill or has to be out of the classroom, a substitute teacher is called in.
Some subs are very good.
I'm sure that you, the students, know what it takes. Be realistic and serious in your descriptions and explanations. Write two paragraphs describing what a good sub does, or what he or she is like. You may want to create a list or web to get you started brainstorming. Feel free to use the back of this sheet to make your plans.