Question

animals give off ____ when they breathe out.
o nitrogen
o carbon dioxide
o oxygen
o hydrogen
question 13
burning fossil fuels adds extra ____ to the air.
o hydrogen
o oxygen
o nitrogen
o carbon dioxide

Explanation:

Animals take in oxygen and give out carbon - dioxide during respiration. Burning fossil fuels releases carbon - dioxide into the air as they contain carbon compounds.

Answer:

For the first question: B. carbon dioxide
For the second question: D. carbon dioxide