Answer:water
Explanation:
water is the most important essential nutrient It is involved in many of your body's vital functions, and it distributes other essential nutrients to your cells.
The correct answer is A only. The A arrow indicated the direction of a gradient of increasing solute concentration in the interstitial fluid surrounding a nephron. Nephron is the basic function of the kidney that is why it is important to indicate the direction of the concentration gradient in which high solute concentration may take place.