Answer:
the correct option is: b) Relaxation of the diaphragm
Step-by-step explanation:
During exhalation or exhalation ALL the muscles of the thorax cavities relax, unless it is a forced expiration there they will not be relaxed, but this is a voluntary and infrequent process.
The relaxation of the diaphragm is what generates an increase in intrapulmonary pressure and therefore it is forced to release its pressure by releasing air through the respiratory tube.
Although it is also valid to say that the internal intercostals are relaxed, since it is true! And it would also be considered as correct, but the diaphragm being a muscle of greater size and greater power generates a more significant effect on the exhalation, that is why it was decided to choose that as the correct option.