(a) Nostrils →larynx →pharynx →trachea →lungs
(b) Nasal passage →trachea →pharynx →larynx →alveoli
(c) larynx →nostrils →pharynx →lungs
(d) Nostrils →pharynx →larynx →trachea →alveoli
The answer is (d) Nostrils →pharynx →larynx →trachea→alveoli
Explanation: Air enters the respiratory system through the nostrils, then travels through the pharynx, larynx, trachea, and alveoli. Following inhalation, the diaphragm and intercostal muscles contract, while the thoracic muscles expand, creating adequate space for air to enter the lungs.