Answer:
A large oasis in the desert. Come with cash and leave with none. What am I?
I have a neck and no head, two arms but no hands. I'm with you to school, I'm with you to work. What am I?
What is black when you buy it red when you use it and gray when you throw it away?
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
I am the noblest musical instrument
No matter how little or how much you use me, you change me every month.