This passage describes a chemical reaction. Read the passage. Then, answer the question below.

As the cells in your body break down food, a poisonous substance called ammonia (NH3) begins to build up in your blood. To reduce the amount of ammonia in your blood, your liver combines ammonia with carbon dioxide (CO2) and other substances to make urea (CH4N2O). The urea later leaves your body as waste.

In the chemical reaction described in the passage, which of the following are reactants? Select all that apply.

Answers: carbon dioxide (CO2), urea (CH4N2O), ammonia (NH3)