Select the correct statement about hormones and their actions

Parathyroid hormone (PTH) stimulates the reabsorption of $\mathrm{Ca}^{2+}$ by renal tubules and increases $\mathrm{Ca}^{2+}$ absorption from digested food. It means PTH increases the blood $\mathrm{Ca}^{2+}$ level. Old aged persons have weak immunity because thymus is degenerated in old individuals resulting in a decreased production of thymosin. Oestoporosis in women occurs due to decreased level of estrogen.