Which phrase best describes effective breathing?

The phrase "calm and steady airflow" accurately describes effective breathing because it emphasizes the characteristics of normal ventilation. Effective breathing involves the ability to take in sufficient air consistently and effortlessly, allowing for proper gas exchange within the lungs. This means the individual can inhale and exhale without difficulty, maintaining a steady rhythm and appropriate depth of breaths.

In contrast, the other options indicate disruptions or inefficiencies in breathing. "Barely breathing" suggests inadequate airflow, which can lead to insufficient oxygen intake. "Gasping for air" reflects a state of distress and potential respiratory failure as it indicates a struggle to breathe effectively. Meanwhile, "only a slight sound" could imply shallow or ineffective breathing, which may not provide adequate ventilation. Thus, the emphasis of the correct answer on calmness and steadiness underscores the essential qualities of effective, healthy breathing.