Biodiversity encompasses the number of: a. ecosystems in a region and number of species in the ecosystem. b. ecosystems in a region, species in an ecosystem, and genes and alleles in a species. c. ecosystems in a region. d. species present in an ecosystem. e. genes and alleles in a species.

b. ecosystems in a region, species in an ecosystem, and genes and alleles in a species.

Explanation:

Biodiversity has three levels - ecosystem, species and genetic diversity. Therefore, Biodiversity  can be defined as the variability among living organisms involving terrestrial, marine, and other aquatic ecosystems, genes and alleles in a species and their ecological complexes such as diversity within species, and between species of the ecosystems.

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.