Answer:
I am a busy worker who is a water mammal.
Brown I am and much admired. Many horses have I tried. Tire a horse and worry a man, tell me this riddle if you can. What am I?
I have no voice but I can teach you all there is to know. I have spines and hinges but I am not a door. Once I’ve told you all I cannot tell you more.
I can only be played on a windy day. What am I?
I am higher than the king. What am I ?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.