In the Late Portion of the Proximal Tubule,part of Na⁺

In the late portion of the proximal tubule,part of Na⁺ reabsorption is passive,through the paracellular pathway.What is the primary driving force for this passive reabsorption of Na⁺?

A) The fact that lower luminal hydrostatic pressure is lower than peritubular hydrostatic pressure
B) The fact that luminal [Na⁺] is higher than peritubular [Na⁺]
C) The fact that transepithelial voltage is lumen-positive
D) The fact that the oncotic pressure of interstitial fluid is lower than that of luminal fluid