Answer:
What body part is pronounced as one letter, but written with three, only two different letters are used?
I go inside boots and outside shoes. What am I?
I cannot be felt seen or touched. Yet I can be found in everybody. My existence is always in debate. Yet I have my own style of music.
I sleep by day, I fly by night. I have no feathers to aid my flight. What am I?
What goes up and down but does not move?
No matter how little or how much you use me, you change me every month.