Final answer:
Infectious diseases come on suddenly and are often contagious. Examples include the common cold, influenza, and mononucleosis.
Step-by-step explanation:
Infectious diseases come on suddenly and are often contagious.
These diseases are caused by pathogens, such as bacteria or viruses, that can be transmitted from person to person.
Examples of infectious diseases include the common cold, influenza, and mononucleosis.