Which of the following organisms possesses the most developed respiratory system?

The location of the pleural fluid is .....

Select the correct statements about alveoli from the following.
$i$. Air sac of each terminal bronchiole shows $10$ to $12$ alveoli.
$ii$. Each alveolus is surrounded by a network of capillaries.
$iii$. They are lined by ciliated pseudostratified epithelium.
$iv$. They provide surface area for exchange of gases.
$v$. There are about $700$ million alveoli in the lungs.

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

The trachea and bronchi are provided with $C$-shaped cartilaginous rings which:

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