Answer: The myelinated nerve fibres are enveloped with Schwann cells, it form a myelin sheath around the axon.
Unmyelinated nerve fibres is enveloped by a Schwann cell that doesn't form a myelin sheath around the axon, and  found in autonomous and the somatic neural systems. Sympathetic Nervous system is part of Autonomous Nervous system. 
Explanation:
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The correct answer is<span> a. Volcanic glass
Volcanic glass is also known as Obsidian. It is formed when lava cools down too rapidly and crystals grow minimally, without grains.</span>
        
             
        
        
        
The Fallopian tubes, or the oviduct, is the passageway through which an egg travels through the ovary to the uterus. The end of the Fallopian tubes have <span>an opening near the ovary called the </span><span>fimbria!</span>