Answer:
What word is a plural, but when you add an "S" to the end, it becomes singular?
What is lengthened by being cut at both ends?
I go around in circles, but always straight ahead. Never complain, no matter where I am led.
A man who was outside in the rain without an umbrella or hat didn’t get a single hair on his head wet. Why?
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
You use it between your head and your toes, the more it works the thinner it grows.