The thoracic cavity increases in volume primarily due to the contraction of which of the following?

Select the correct process that occurs during inspiration (inhalation):
$(a)$ Contraction of the diaphragm
$(b)$ Contraction of external intercostal muscles
$(c)$ Decrease in pulmonary volume
$(d)$ Increase in intra-pulmonary pressure

Select the correct statement.

State the sequence of events for inspiration (breathing in).
$I$ - Increase in lung volume
$II$ - Decrease in intrapulmonary pressure
$III$ - Contraction of respiratory muscles
$IV$ - Increase in thoracic volume
$V$ - Air rushes into the lungs

An $A$ in the pulmonary volume $B$ the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from $C$ to move into the lungs,i.e.,$D$. Choose the correct options for the blanks $A, B, C$ and $D$ to complete the above statement with reference to $NCERT$ textbook.

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