The correct option is B Osmoregulation.
Osmoregulation is the active regulation of the osmotic pressure of a cell to maintain water content; that is, required to keep cell's osmotic pressure at an optimum level and cytoplasm neither too diluted or too concentrated.
A membrane which allows the passage of a solvent but not of a solute is called semipermeable membrane whereas a membrane which permits passage of one substance more easily than another is called selectively permeable which is characteristic of the cell membranes. The plasma lemma is selectively permeable and selects the solutes which can flow in or move out. Thus, plasmalemma helps in maintaining osmotic balance or osmoregulation of a cell.