Inspiration is initiated by

Given below are events occurring during inspiration. Select the correct order of sequence from the options given below.
$(I)$ Air from atmosphere rushes into lungs.
$(II)$ Thoracic volume increases.
$(III)$ Intercostal muscles contract and ribs along with sternum move upward and outward.
$(IV)$ Diaphragm becomes flat and goes downwards.

Pick the correct statement.

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

What happens during expiration?

The ventilation movements of the lungs in mammals are governed by: