Practice question

The correct answer is C: Water and ions. In Digestive System, this idea is central because it matches how the body actually works in everyday teaching examples. Put simply, the functional job described in the stem is exactly what Water and ions does in Digestive System. That is why Water and ions is the option that holds up when you check it against basic physiology. When you revise, say the answer out loud with one short reason attached; that sticks better than rote lists. Remember that physiology questions reward precise language: name the process, the location, and the outcome, then match that to the option text.