Final answer:
Adler's three-word definition for the germ theory of disease aligns closely with the option 'Microorganisms cause disease', which reflects the theory's assertion that diseases are caused by pathogenic microorganisms or germs.
Step-by-step explanation:
The germ theory of disease is a scientific theory that suggests that many diseases are caused by microorganisms. These microorganisms, also known as pathogens or germs, include entities such as bacteria and viruses that can grow, reproduce, and cause illness in their hosts. Infectious diseases are therefore caused by the transmission and growth of these pathogens.
Adler's three-word definition for the germ theory of disease is not explicitly provided in the provided reference material, but based on the information given, the closest option that encapsulates the germ theory of disease would be 'Microorganisms cause disease', which aligns with the historical perspectives provided by scientists like Girolamo Fracastoro and Robert Koch, both of whom contributed significantly to the development and understanding of this theory.