Answer:
What goes through a door but never goes in. And never comes out?
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
A harvest sown and reaped on the same day In an unplowed field, Which increases without growing, Remains whole though it is eaten Within and without, Is useless and yet The staple of nations.
Who is he that runs without a leg. And his house on his back?
What has two legs but doesn't walk?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.