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?

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

Hi!

The correct answer would be:

It provides an explanation for many observations and accepted hypotheses.

Explanation

A law is a statement of fact that differs from a theory or hypothesis in that it does not provide an explanation for a phenomenon. It does not change over time, and there are no exceptional cases in it. For instance, a day is 24 hours long. It is an obvious, observable fact. There are no explanations, or exceptions - no days where the day is less or more than 24 hours long.

Now, a theory is an explanation of a hypothesis or an observation or phenomenon. A hypothesis is known to be the reason behind a certain observation, and if  the hypothesis survives scrutiny and tests, it is established as a theory - but it may be replaced by better theories or grow obsolete over time, such as the atomic theory which stated that atoms were the smallest indivisible particle in nature.

he made 11 calls in one day

the answer is b, have negligible mass