Answer:
I have a head, tail, but no arms and legs. What am I?
I get dirty when wiping things clean. What am I?
The more it dries, the wetter it becomes. What is it?
My second is performed by my first. A thief by the marks of my whole might be caught. What am I?
I help you carry your books.
No matter how little or how much you use me, you change me every month.