Answer:
how many letters are there in the alphabet
My first is in blood and also in battle. My second is in acorn, oak, and apple. My third and fourth are both the same. In the center of sorrow and twice in refrain. My fifth starts eternity ending here. My last is the first of last, Oh Dear.
This is in a realm of true and in a realm false, but you experience me as you turn and toss.
What is as big as you are and yet does not weight anything?
I have four wings but cannot fly. I never laugh and never cry. On the same spot always found, toiling away with little sound.
You use it between your head and your toes, the more it works the thinner it grows.