Answer:
I am as hard as metal, yet as flimsy as glass. I shine like a star, yet I am only a rock. What am I?
I am a band that does not perform sing or act.
I see what you see feel what you feel and hear what you hear. I know all of your moves before you make them. I even know the moves you didn't make.
Two bodies have I, though both joined in one. The more I stand still the faster I run. What am I?
I am the thing that is used to make your weight. What am I?
No matter how little or how much you use me, you change me every month.