The conservation of energy is a because it is has been demonstrated without exception under certain stated conditions.
a. scientific theory
b. scientific variable
c. scientific hypothesis
d. scientific law

I think it is D

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D. scientific law

Explanation:

A scientific law is a statement which is based upon the natural process, phenomena or event which is based upon repeated trials of experiments. But it does not explanation for the cause of natural process or phenomena or event. The scientific law is abide by all the scientific communities and it cannot be changed or manipulated.

The conservation of energy is a scientific law. As it cannot be changed and it is demonstrated without including any exception under any condition.        

it cools slower in the earth meaning the crystals have more time to form than lava on the surface

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.