What happens to a unit when you divide it by itself? (I.e. kJ/kJ)

Your answer if I'm assuming you have the multiple choice like I did in my quiz would be : The two units cancel out.

Explanation:

The reason is Kilojoule (kJ) is equal to 1000 joules. So what you do is just divide 1,000 by 1,000. When you do that both cancel out each other because they're the same and you're left with 1.

Hope this helps that's how I figured out my answer, sorry if I'm late.  

Here is a picture of my answer

The correct answer is A:  Carbon enters the atmosphere as carbon dioxide from respiration and combustion.