$A$ pair of external nostrils present in humans opens out

The cilia of the trachea transfer:

The correct sequence of the following parts of the lower respiratory system is:
$I.$ Bronchi $\quad$ $II.$ Larynx
$III.$ Bronchioles $\quad$ $IV.$ Alveolus

The portion of the vestibule between the true and false vocal cords is known as:

The nasal cavity and the oral cavity are separated from each other by the:

Identify the component of the respiratory system which displays the features given below and choose the correct option:
$I.$ Double layered
$II.$ Fluid contained in it reduces the friction on the lung surface
$III.$ Its outer layer is in contact with the thoracic wall
$IV.$ Its inner layer is in contact with the lungs