\begin{table}%t4
 %\centering
\par
  \caption {\label{tab: class}Summary of classification schemes.}
  \begin{tabular}{lll}
\hline\hline
\noalign{\smallskip}
Scheme & Classification & Acronym \\ \hline
\multirow{3}{*}{Entropy ratio}      & Low-Entropy Core    & LEC \\
                                    & Medium-Entropy Core & MEC \\
                                    & High-Entropy Core   & HEC \\
\multirow{3}{*}{Core properties}    & Cool Core           & CC  \\
                                    & Intermediate        & INT \\
                                    & Non-Cool Core       & NCC \\
\multirow{2}{*}{Dynamic properties} & No Observed Merging & NOM \\
                                    & Merging System      & MRG \\
\hline
\end{tabular}
\end{table}