There are microvilli on the luminal apical) surface of the epithelium that lines the lumen of the proximal tubule. Microvilli are structural features designed to

A) maximize surface area available for reabsorption of solutes from the renal tubule.
B) accommodate membrane proteins involved in active transport of substances into the rental tubule.
C) maximize surface area available to pump ions into the renal tubule.
D) provide adequate space to house membrane proteins involved in active transport of solutes out of the renal tubule.