Sickle cell anemia is a painful and often lethal (deadly) disease. individuals with sickle cell anemia have shorter than average lifespans and have fewer than average children. and yet, despite these obvious and severe disadvantages, about four million people worldwide have it. how can a trait that directly limits an individual's evolutionary fitness (reproductive success in a particular environment) still be so common? in this lesson, you will discover the answer using your knowledge of genetics, data analysis, and evolution. what to do read "sarah's story. then, answer the analysis questions, refer to the bite in your answers when needed.

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.

well, i believe that the answer is 2. : 3