What began as a single fertilized egg has just separated into two distinct eggs. this indicates the formation of twins that has occurred during the period of development?

The above statement indicates the formation of monozygotic twins that has occurred during the blastocyst period of development.

Explanation:

When a single fertilized egg has just separated into two distinct eggs, it indicates the formation of monozygotic twins that has occurred during the blastocyst ( 2 celled) period of development  

Usually a female during the mensural cycle releases one egg from one of the fallopian tube, whereas 1% of the females release 2 eggs from the fallopian tubes causing the formation of dizygotic twins but if it is from a single egg then they are said to be mono-zygotic twins.

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.

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.