Which of these allowed Robert Koch to demonstrate that a specific microorganism causes a specific disease? A. The microorganism is found in only some animals that have the disease. B. The microorganism is found in both sick and healthy animals. C. Healthy animals become sick when exposed to the microorganism from unhealthy animals. D. Unhealthy animals become healthy when cohabiting with animals immune to the microorganis

The correct answer is:<br /><br />C. Healthy animals become sick when exposed to the microorganism from unhealthy animals.<br /><br />This principle is known as Koch's postulates, which are a set of criteria used to establish a causal relationship between a microorganism and a disease. According to these postulates, for a microorganism to be considered the cause of a disease, it must be found in all cases of the disease, isolated from the diseased host and grown in pure culture, and when introduced into a healthy organism, it should cause disease.