Choose the pair of elements that play a role in normal functioning of cell membranes.

Calcium and Boron are involved in normal functioning of membrane. Iron is essential for the formation of chlorophyll and also a part of enzymes like nitrogenase and electron carriers like cytochromes and ferredoxin. Manganese is activator of some oxidoreductases. Magnesium is cofactor of several oxidoreductases. Potassium helps in maintaining the turgidity of cells and also plays a role in stomatal movement.