Which respiratory muscle(s) function(s) only during forced expiration?

A) Diaphragm
B) External intercostals
C) Pectoralis major
D) Pectoralis minor
E) Internal intercostals

The internal intercostals are the respiratory muscles that function only during forced expiration. They pull the ribs downward and inward, decreasing the volume of the thoracic cavity, which increases the pressure inside the lungs and causes air to be expelled. The diaphragm and external intercostals function during both normal and forced breathing, while the pectoralis major and minor are not respiratory muscles.