Which of the Following Statements Is True

Which of the following statements is true?

A) In smooth muscle contraction, the roles of calcium and magnesium are antagonistic, with calcium promoting the process and magnesium being the inhibitor if bound to sites that are normally occupied by calcium.
B) Magnesium promotes phosphorus absorption.
C) Calcium and magnesium promote each other's reabsorption in the kidney.
D) Calcium may cause an alteration in magnesium distribution by changing the flux of magnesium across the cell membrane or displacing it on its binding sites.