The chemical composition of Plaster of Paris is

A

$$CaSO_{4}. \frac{1}{2}H_{2}O$$

B

$$CaPO_{3}. \frac{2}{3}H_{2}O$$

C

$$CaPO_{4}. 4H_{2}O$$

D

$$CuSO_{4}. 3H_{2}O$$