They can be solids, liquids, or gases. They come in different sizes and shapes. They combine in different numbers and ratios. They can be a proton, a neutron, or an electron.
I gave my students this multiple choice question: The elements carbon, hydrogen, and oxygen are parts of many different compounds. Which explains why these three elements can make so many different compounds?

Only one answer is correct among these 4 choices:
- They can be solids, liquids, or gases.
- They come in different sizes and shapes.
- They combine in different numbers and ratios.
- They can be a proton, a neutron, or an electron.

Could you tell me which one is correct?

They combine in different numbers and ratios.