On an average,a healthy human breathes $......$ times per minute.

What happens during expiration?

Lung ventilation movements are due to

In mammals,the ventilation movements of the lungs are governed by:

$I.$ Intra-pulmonary pressure remains less than the atmospheric pressure.
$II.$ There is negative pressure in the lungs compared to the atmospheric pressure.
In which of the above two situations does inspiration take place? Choose the correct option.

Which one of the following is a possibility for most of us in regard to breathing,by making a conscious effort?