Final answer:
A pandemic is an epidemic that has spread over multiple countries or continents, affecting a large number of people worldwide; an epidemic is more localized.
Step-by-step explanation:
The difference between pandemics and epidemics is in their scale and reach. An epidemic is when a disease affects a large number of people within a community, region, or population at the same time. On the other hand, a pandemic is an epidemic that has spread over multiple countries or continents, usually affecting a large number of people worldwide. Therefore, the correct answer to the question is B. Pandemics affect many countries or states; an epidemic is more localized. Diseases like influenza can lead to both epidemics and pandemics, depending on the number of people infected and the regions impacted.