Answer the following question given this paragraph: 

When we run a reaction to produce a gas, we expect it to rise into the air. Many students have done experiments where gases such as hydrogen are formed. The gas can be trapped in a test tube held upside-down over the reaction. Carbon dioxide, on the other hand, sinks when it is released. Carbon dioxide has a density greater that air, so it will not rise like these other gases would.


Q: Carbon dioxide does not rise like other gases because it has a density greater than what?

 Choices:

- gravity

- light

- water

- air

A:
air
