Which sequence most accurately describes the sequence of airflow in the human respiratory system?
1. pharynx 2. bronchus 3. trachea 4. larynx 5. alveolus
6. bronchiole
$(a) 4,1,3,2,5,6$
(b) $1,4,3,2,5,6
(c) 4,1,3,2,6,5$
$(\mathrm{d}) 1,4,3,2,6,5$
(e) 1,3,4,2,6,5.