$A$ healthy human breathes $........$ times per minute.

If there is a puncture in the thoracic cavity but not in the lungs,then...

$A$: Normal expiration during quiet breathing,unlike inspiration,is a passive process because no muscular contractions are involved.
$R$: Normal expiration results from the elastic recoil of the chest wall and lungs.

When do the expiratory muscles contract?

What is the most important function of the diaphragm in mammals?

The lungs do not collapse during breathing and some air always remains in the lungs which can never be expelled because: