Answer:
I am the key that is the hardest to turn
I am an instrument that you can hear but cannot see or touch. What am I?
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.
I will disappear every time you say my name. What am I?
I run up and down the stairs without moving. What am I?
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.