Which membrane covers the lungs and provides protection?

The lungs contain a large number of narrow tubes known as:

Describe various parts of the human respiratory system.

What is the function of the liquid present between the pleural membranes?

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

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