After darwin proposed his ideas about natural selection as a mechanism for evolution, it took time before evolution was generally considered a theory. why do we now refer to it as a theory?

It is a fact and not a theory

Explanation:

A scientific theory is some natural phenomenon that has been tried and tested several times and backed by logical and testable observations and hypotheses in a way that  in future anyone can test it. It is not a guess or hunch but a concept explained with logic and backed by solid unvarying proofs.

In case of biological evolution, observations have been made and tested several times so that no more further testing or trying is required. Hence, by this logic evolution can be considered as a fact but it can not be considered as a theory.

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explanation:

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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.