Answer:
What goes up and down stairs without moving?
Curtail me thrice I am a youth; behead me once a snake; complete I'm often used in truth when certain steps you'd take.
David's father has three sons: Snap Crackle and ?
I am always in front of you, but you will never see me. What am I?
What goes through a door but never goes in and never comes out?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.