The correct answer is microglia.
<span>Microglia is glial cells found in the central nervous system with the protective role. Because they are the resident macrophage cells, they act as the first and main form of active immune defense. Microglia is constantly cleaning the CNS for plaques, damaged or unnecessary neurons, and infectious agents, like viruses or other microorganisms.</span>
Years would be the independent variable because any sort of time is usually the independent variable.
DNA is where genetic information is stored
Answer: gametes, sperm, meiosis
