Answer:
Actually, D is the correct answer
The CNS are lined by ependymal cells. Ependymal cells are epithelial cells that monitor the composition of cerebrospinal fluid (CSF)
Your answer is precipitation: <span>Any or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere (e.g., rain, hail, snow or sleet). It is a major class of hydrometeor, but it is distinguished from cloud, fog, dew, rime, frost, etc., in that it must fall. It is distinguished from cloud and virga in that it must reach the ground.(Grammarly)</span>
