\documentclass[12pt]{article}
\begin{document}
\begin{tabular}{ccccccc}
$D_1$~~~~~~ &  $D_2$~~~~~~  &   $D_3$~~~~~~   & $ D_4$~~~~~~   & $\cdots$~~~~~~   &
$D_{2L-1}~~~~~~$  &
$D_{2L}
$ \\
\\
$W_1$~~~~~~ &  $W_2$~~~~~~  &   $W_3$~~~~~~   & $ W_4$~~~~~~   & $\cdots$~~~~~~   &
$W_{2L-1}~~~~~~$  &
$W_{2L}
$ \\
\\
$Y_1$~~~~~~ &  $Y_2$~~~~~~  &   $Y_3$~~~~~~   & $ Y_4$~~~~~~   & $\cdots$~~~~~~   &
$Y_{2L-1}~~~~~~$  &
$Y_{2L}
$ \\
\\
\end{tabular}

\end{document}