Final answer:
The correct option is C). Water accounts for 50-70% of an adult's body weight, depending on various factors like age and body composition, and plays numerous essential roles in bodily functions.
Step-by-step explanation:
Water constitutes 50-70 percent of the body weight in adults. This varies depending on factors such as age and body composition. Infants, for example, have a higher percentage of about 75%, while in adults it ranges around 50-60%, and may decrease to as low as 45% in old age. It is important to note that water content is not uniformly distributed in the body; some organs like the brain and kidneys have the highest proportions, comprising 80-85 percent of their masses.
Within the body, water plays several crucial roles: it functions as a major component of intracellular and extracellular fluids, acts as a lubricant and cushion, is vital for numerous cellular reactions, assists in digestion and circulation, supports the nervous system, helps regulate body temperature, and aids in flushing out bacteria and viruses. A balance of water is maintained through a process known as osmosis, where water moves through semi-permeable membranes to areas of higher solute concentration to maintain equilibrium.