Answer:
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
Three little letters. A paradox to some. The worse that it is, the better it becomes.
You will find me with four legs, but no hair. People ride me for hours, but I don't go anywhere without needing to be tugged. Jerked or turned on, I always manage to be ready for work.
I have four legs but no tail. Usually I am heard only at night.
There is a puzzle which can be asked all day with a different correct answer each time. What is the puzzle?
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?