According to anthropologist Helen Fisher, romantic love between two partners in prehistoric times seemed to wane about years into the partnership.

Four.

Explanation:

Helen Fisher describes romantic love "as a very primitive, basic human emotion as basic as fear, anger or joy". She explained that men and women in prehistoric times who were in love were bound together in preparation for child bearing. But, after four years of raising a child through infancy, the love that once existed begins to wane. The couples tend to break up and search for new partners.

scientists have discovered that hiv does not cause aids by the virus's direct effect on the host's immune cells, but rather through the cells' lethal influence on one another. researchers from the gladstone institutes have revealed that hiv does not cause aids by the virus's

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.