system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are we referred to as carbon-based life forms?

When we're 70% hydrogen and oxygen molecules?
gpt
Carbon can make 4 molecular bonds, oxygen can make 2, and hydrogen can make only 1.  While oxygen and hydrogen have their place in many processes, carbon forms the backbone and structure of all complex organic molecules.  

Imagine trying to make a marshmallow-and-toothpick structure where each marshmallow could only have one or two toothpicks attached to it.  You couldn't make anything more complex than a ring or line.  Now try it where you can have some marshmallows with 3 or 4 toothpicks.  Now you're getting somewhere.  Now you can make all sorts of things.  That is why we are considered carbon-based.