Ascientific theory is

a. a hypothesis that has been rigorously tested and never been disproven.
b. a hypothesis that has been rigorously tested and only been disproven a few times.
c. an opinion.
d. a hypothesis that has been tested at least five times.
e. an idea based on a person's experience or knowledge.

The correct answer is A. a hypothesis that has been rigorously tested and never been disproven.

Explanation:

A hypothesis is an idea or guess or a proposed explanation of any phenomena. When the hypothesis is checked and proved by many experiments and cannot be disproven by anyone then it considered as a scientific theory.

Therefore a scientific theory is a hypothesis that has been rigorously tested by the performing different experiments and never been disproven. For example theory of evolution, natural selection which tell us about the evolution of organism on earth which is proven by Darwin. So the right answer is A.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.