The correct option is B active transport
Urine formation involves three processes - ultrafiltration, reabsorption and secretion. Reabsorption is necessary to prevent loss of essential nutrients in urine. Around 99 percent of filtrate formed is reabsorbed. The epithelial cells of renal tubule reabsorb these substances either by active or passive mechanisms. Substances like glucose, amino acids, Na+, are reabsorbed by active transport. Substances like nitrogenous wastes and water are reabsorbed passively.