Final answer:
Pneumonia is the disease caused by a pathogen, while rickets, scurvy, and diabetes are not pathogen-related.
Step-by-step explanation:
The disease caused by a pathogen among the choices given is pneumonia. Pneumonia results when the air sacs in the lungs, known as alveoli, become inflamed and fill with fluid due to infection. In contrast, rickets is caused by vitamin D deficiency, scurvy is due to a lack of vitamin C, and diabetes is generally a metabolic disorder related to insulin production or use, rather than a pathogenic infection.