The following graph depicts the changes in tubular fluid concentrations of various substances along the length of the proximal tubule,plotted as the tubular fluid-to-plasma concentration ratio (TF/P).Thus the TF/P = 1 for a substance that is at the same concentration in the tubular fluid and plasma (for all substances that are freely filtered,TF/P = 1 at the glomerulus). Match the following substances to the appropriate TF/P curve. Na⁺