Different microscopic organisms cause different diseases. when a dangerous microscopic organism is transferred from one person to many people, the disease it carries will spread.

why is this considered a theory instead of a hypothesis or a law?

a. it is a statement of fact about how nature works instead of an explanation.
b. it provides an explanation for many observations and accepted hypotheses.
c. it describes how to test a possible explanation of one specific relationship.
d. it has not changed over time even though new technology has been developed.