According to scentific thought, what is a theory?

Explanation:

A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world.

First you would start with a hypothesis, which is an idea that hasn't been proven yet.

If enough evidence accumulates to support the hypothesis, it moves to the next step — which is a theory — in the scientific method and becomes accepted as a valid explanation of a phenomenon.

A theory is something that has scientific method behind it and it is accepted by the scientific community as a valid explaination of a phenomenon.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).