I wish to type this table in REVTex, however, the code below does not work for \documentclass{revtex4} but only for \documentclass{article}:
\documentclass{revtex4}
\usepackage{array,mathtools,amssymb,booktabs}
\newcolumntype{C}{>{$}c<{$}}
\begin{document}
\begin{tabular}{cCCC}
\toprule
\multicolumn{2}{c}{} & K & H\\\midrule
A & a & 1& 4\\\cmidrule(lr){2-4}
B & b & 2 & 5\\\cmidrule(lr){1-4}
\multicolumn{2}{c}{C}& 3 & 6\\\bottomrule
\end{tabular}
\end{document}
The code is from the source of this page. Thanks to the generous cfr.