Step-by-step explanation:
The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to be seen without magnification, invade humans, other animals, and other living hosts. Their growth and reproduction within their hosts can cause disease ¹.
Based on this information, it seems that option C: "one infectious agent causes one disease" is the closest to the germ theory of disease.