Which term is used to describe a fact that has always been observed true but could at some future time not be observed as true.

a) hypothesis
b) theory
c) law

Theory would refer to a concept or idea that is, at one point, considered a fact, but that could be disproven in a future setting. A hypothesis would not be used to describe a fact, and a law is something that is more concrete. The theory, however, is a perception based on an array of experiments that allow such a notion to come forth, but can be disproven with future knowledge or understanding.