What’s the main part of the nervous system a. nerves b. spinal cord c. the brain d. brain steam

The main part of the nervous system is the C. the brain, which controls all your movements, thinking, and such. After the brain is the B. spinal cord, which helps transmit the messages from the brain to the body parts, as well as vice versa.

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genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).