What percentage of nitrogen bases are in cytosine if the strand has 40% thymine?

plus 20% is 40% of adennine and thymine. From 100% DNA bases subtract 40% and you will get 60%. Then divide this by 2 and you will get 30%. 30% of guanine and 30% of cytosine, because their amounts are equal in the DNA stand.

weathering is the answer.

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.