When Na⁺ is actively transported from tubular cells to the interstitial fluid,

A) no energy is needed.
B) glucose and amino acids are countertransported at the same time.
C) Na⁺ concentration gradient is established between the tubule lumen and tubule cell.
D) water is countertransported by carrier molecules.
E) water is secreted.

The active transport of Na⁺ (presumably a typographical representation of sodium and another substance) from tubular cells to the interstitial fluid establishes a concentration gradient between the tubule lumen and tubule cell, as active transport typically moves substances against their concentration gradient, requiring energy and thus establishing a gradient.