Choose one of the following three diagrams. Specify your choice here:_ (a, b, or c). Identify the system(s) your diagram represents, and the parts associated with that system.

b. Motor Unit

Explanation:

A motor unit is consist of motor neuron and muscles fibers connected through the axon terminal of neuron. Motor unit function for the movement (contraction and relaxation) of muscles.

A neuron is connected with muscles fiber through the axon terminal of neuron and is called neuromuscular junction. Skeletal muscle fiber is consist of a cylindrical muscle cell that contain microfibrils which participate in contraction and relaxation of muscles.

Neuron and muscle fiber coordinate with other other for the proper functioning of motor unit.

Hence, I selected diagram "b" that represents motor unit.

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.