A.  Fine Focus.
B.  Nucleus, Cytoplasm, and membrane
C. 30 Micrometer.
Erythrocytes are well known to have no nucleus but in fact, they lack most organelles such as the Golgi apparatus endoplasmic reticulum and mitochondria. Hair consists of two parts the root and the hair shaft. The root is the part of the living hair located in the middle layer of the skin the dermis. 
Epidermal root cells in some plants produce root hairs and tubular growths that increase the surface area of the root. Unlike other cells in the body, red blood cells do not have a nucleus. This habit dates back to when mammals began to evolve. Other vertebrates such as fish reptiles, and birds have erythrocytes that contain dormant nuclei. To allow red blood cells to carry an increased load of oxygen cells evolved to function without a nucleus and other associated organelles.
Learn more about Cell Types here:-brainly.com/question/342784
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<span>presence of protoplasm, self built organisms, self repair, reproduction and various life process like metabolism, nutrition, respiration, exchange of material, transportation, excretion and irritability.</span>
        
                    
             
        
        
        
Unsaturated fatty acids are a component of the phospholipids in cell membranes and help maintain membrane fluidity. The Phospholipids contain a variety of unsaturated fatty acids, when compressed, the “kinks” in their tails push adjacent phospholipid molecules away, that helps in maintain fluidity in the membrane. Unsaturated fatty acids have at least one double bond, creating a "kink" in the chain, the absence of double bonds decreases fluidity, making the membrane very strong and stacked tightly.
The ratio of saturated and unsaturated fatty acids determines the fluidity in the membrane at a temperature, at appropriate temperatures the phospholipids have enough kinetic energy to overcome the intermolecular forces holding the membrane together, which increases membrane fluidity.
To learn more about Unsaturated fatty acids , here
brainly.com/question/4891995
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C. Gradual
Hope this helps!