* Cellular respiration is the process where cells break down glucose (sugar) in the presence of oxygen to release energy in the form of ATP (adenosine triphosphate).

Let's look at the other options:

* A Oxygen: Oxygen is actually *used* during cellular respiration, not released.

* B Air: Air is a mixture of gases, including oxygen, which is used in respiration.

* D Lactic acid: Lactic acid is produced during anaerobic respiration (when oxygen is limited), not the primary form of cellular respiration.

In summary: Cellular respiration releases energy (ATP) as a byproduct of breaking down glucose.