Easy Riddles and Answers

Question: How can you add 9 to become 6? (No subtracting).

Question: I break down buildings I crumble mountains You can't see me What am I?

Question: What goes up and down but never moves?

Question: What goes around comes around?

Question: I am important at the most dangerous times. I can not be seen, heard, or smelled. If you use me too much you would fatally die. What am I?