What function SPECIFICALLY causes air to enter the lungs?
a. The diaphragm pushes air into the lungs.
b. The difference in air pressure between the lungs and outside air during inhalation.
c. The decrease in size of the chest.
d. The movement of air over the pharynx.

Muscles in your chest and abdomen contract, or tighten, to create space in your lungs for air to flow in. The muscles then relax, causing the space in the chest to get smaller and squeeze the air back out.

Inspiration (breathing in).

The diaphragm contracts and moves downwards. The intercostal muscles contract and move the ribs upwards and outwards. This increases the size of the chest and decreases the air pressure inside it which sucks air into the lungs.