Scientific theories are always . a theory may be changed as a result of ?

Scientific theories are always testable. A theory may be changed as a result of new observations.

Explanation:

A scientific theory is a set of laws, facts and hypotheses that have a complete vision of an aspect of reality. In other words, a scientific theory is a proposed explanation for a set of observable phenomena. It allows in this way to organize and understand the observations and to be able to predict or provoke other future observations.

Any scientific theory must be based on a rational examination of the facts. The facts can be observed and measured, while theories are the scientific explanations and interpretations of those observable facts.

Theories can be modified or improved as more information is collected. That is, theories can continue to be tested indefinitely, and eventually rejected, if the tests lead to it.  Therefore, a scientific theory is testable by using a research method.

As mentioned, any theory can be tested or rejected as more information is collected. This information to prove or reject theories are interpretations of observable facts, which generates new statements or allows to accept those already included in the theory. Then, a theory may be changed as a result of new observations.

Finally, scientific theories are always testable. A theory may be changed as a result of new observations.

the answer is d.) potassium