The correct option is B Assertion and reason are true; reason is the correct explanation of the assertion.
Water is vital for our body functions. It helps in digestion, removal of waste, regulation of body temperature and also acts as a shock absorber. It improves the texture of skin and keeps lungs, mouth and mucous membranes moist. It also keeps the blood thin enough to flow through the blood vessels. So we need to consume enough water in a day as the body cannot store water.