C because mass is how much space an object takes up
1). I started up my car. Gasoline was spritzed into the cylinders, mixed with air, and then exploded with an electrical spark. As the gasoline vapor instantly burned in the air, several new things were formed that weren't there before, like carbon dioxide, carbon monoxide, water, and oxides of nitrogen.
2). I left my dinner on the stove a little too long, and it got a layer of crunchy crackly sooty carbon on the bottom. That part of it didn't taste too good. This isn't exactly something that happens every day, but more often than I'd like it too.
3). All day, every day, and all night, every night, about 10 or 20 times every minute, I pull air into my lungs. I keep it there for a while, then I blow it out and pull in some fresh stuff. The air I blow out has less oxygen and more carbon dioxide in it than it had when I pulled it in. That's because of the hundreds of chemical reactions going on inside my body, to keep me alive and functioning. I hope these keep going on for many many more days in the future.
