$\begin{array}{1 1} \text{(a) Every pure solid crystalline substance has a characteristic and unique melting point} \\ \text{
(b) Impure sample of substance has different melting point} \\ \text{
(c) Two different pure substances have same melting points} \\ \text{
(d) Melting point serves as the criteria of purity of a solid substance}
\end{array} $
