Which of the following is a very unique feature of the mammalian body?

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

....... are the primary sites of exchange of gases.

Why does the air in the nasal cavity get warmed?

Where are lungs situated in the human body?

The largest cartilage of the larynx is an example of which type of cartilage?