What Am I Riddles

Question: All things I devour: Birds, beasts, trees, flowers.
I gnaw iron, bite steel.
I grind hard stones to meal.

What am I?

Question: I'm number three.
But I'm not a number.
I'm hot and cold at the same moment but not at the same time.
I'm number three.
But I'm not a number.

Who or what am I?

Question: I am something, a lot of people don't like me, including you,but I'm called upon anytime one is injured. I like playing with pregnant women, I'm a 5 letter word, and if my last letter is put before first letter, I become a name of a country, WHAT AM I? IF U GET THIS, U'RE INDEED A GENIUS.

Question: I am apart of everything, including you. Once I die, I will begin anew. As my life status becomes dire, I burn brighter and brighter. What am I?

Question: What has classes but moves?