During inhalation, diaphragm
(a) relaxes and rib muscles contract
(b) and rib muscles both relax
(c) contracts and rib muscles relax
(d) and rib muscles both contract

Correct Answer: (d) and rib muscles both contract

Explanation:

During inhalation, the diaphragm contracts and pulls downward. The rib muscles located between the ribs contract and pull upward. It increases the size of the thoracic cavity and decreases the pressure inside, therefore air rushes in and fills the lungs with air.