\documentclass{article}
\usepackage{lscape}
\thispagestyle{empty}
\begin{document}
\setcounter{equation}{0}
\begin{tabular}{cccc}
A & B & C & D \\
\multicolumn{1}{||c||}{A} & B & C & D \\
A & \multicolumn{2}{||c||}{BC} & D \\
\multicolumn{1}{||c||}{A} &  \multicolumn{2}{|c|}{BC} & D \\
\multicolumn{1}{||c||}{A} &  \multicolumn{2}{||c||}{BC} & D \\
\end{tabular}
\end{document}