An independent variable is a. directly changed by the experimenter b. manipulated by changes to the dependent variable c. a variable that is kept constant d. a variable that is used as a control

A independent variable is a variable which the experimenter can control and by changing the independent variable the experimenter observes or records the value of dependent variable.

so i see if you are asking independent than the answer is A.

if you are asking dependent variable than the answer may be B because manipulated by changes to the independent variable would be the best 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.