The active phase of normal, relaxed breathing is:

A. Epistaxis refers to nosebleed, which is unrelated to lung function or expansion.
B. Effusion refers to the accumulation of fluid (such as pleural effusion, where fluid collects in the pleural space around the lungs), not incomplete lung expansion.
C. Atelectasis is the collapse or incomplete expansion of a lung or part of a lung, which can occur due to blockage, pressure, or injury.
D. Adhesion refers to abnormal fibrous connections between tissues, which can occur in the body after injury or surgery, but it does not refer to incomplete lung expansion

A. Exhalation is the passive phase of normal breathing and occurs without effort during relaxed respiration. It involves the diaphragm and intercostal muscles relaxing, allowing air to flow out of the lungs.
B. Apnea refers to a temporary cessation of breathing and is not a phase of normal breathing.
C. Inhalation is the active phase of normal, relaxed breathing. It requires energy as the diaphragm contracts and moves downward and the intercostal muscles contract to expand the chest cavity, allowing air to enter the lungs.
D. Expiration is another term for exhalation, which is passive during normal relaxed breathing.