What is the cause of altitude sickness?

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

Lung ventilation movements are due to

What happens to the volume of the pulmonary cavity when there is an increase in the volume of the thoracic chamber?

Explain the process of inspiration under normal conditions.