The answer is A) they provide a source of energy.
Explanation:
mice can bite the elephant's trunk and/or feet and they can get the elephants a surprise.
Having one theory is setting a limit on your potential and the potential of the overall theory and subject you are working on. Having multiple theories gives you a broader idea and perspective of what is going on, and even though one may slightly contradict the other, it is okay because that is what theories are for.
To the point, scientists usually have more than one theory so that they can gain a broader perspective on the matter and maybe even increase the chance of being correct on the matter.
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In a study of the raw materials used for photosynthesis, the two molecules that would be studied are carbon dioxide and water. This is because they are the reactants of the process. Without these molecules the process of photosynthesis cannot happen.