Hardening of plaster of paris is because of

Question

$\begin{array}{1 1}(a)\;\text{The formation of }CaCO_3\\(b)\;\text{The formation of }CaSiO_3\\(c)\;\text{The transition of orthorhombic gypsum to monoclinic gypsum}\\(d)\;\text{Dehydration}\end{array}$