You are called to a local soccer complex for a player experiencing sudden chest pain and shortness of breath. The tall, thin male patient tells you that he was lunging to block a shot on goal when the symptoms started. Your assessment reveals that the anterior chest is symmetrical and non-tender, lung sounds are slightly diminished in the right upper lobe, the neck veins are flat, and the trachea is midline. Which of the following is the MOST likely cause of the patient's symptoms?
a. Asthma.
b. Rib fracture.
c. Pulmonary embolism.
d. Spontaneous pneumothorax.