Which term describes the inhalation and exhalation of air?

• A. respiration
• B. restrict
• C. serene
• D. symptom

Answer: (A)

Breathing is called respiration. It describes the cycle of taking air into the lungs (inhalation) and then letting air out (exhalation). This process, driven by the respiratory muscles, enables gas exchange—oxygen moves into the blood and carbon dioxide is expelled. The other words don’t describe this action: restrict means to limit, serene means calm, and symptom is a sign of disease. (Note: cellular respiration is a related term for how cells convert nutrients into energy, but that happens inside cells and isn’t about breathing in and out.)