\begin{table}%t4
%\centering
\par
\caption{\label{tab_extinction}Dust extinction of GRB host galaxies.}
%\label{GRB Host Galaxies emission line fluxes}
\par
\tiny\begin{tabular}{ccccccccccccccc}
\hline\hline    \noalign{\smallskip}
{GRB} & $\rm{H\alpha}/\rm{H\beta}$ & $\rm{H\gamma}/\rm{H\beta}$
& $A_{V}(\rm{H}\alpha/\rm{H}\beta)$ & ${A_{V}}(\rm{H\gamma}/\rm{H\beta}$) & $E_{\rm HG}(B-V)$  \\
\hline
980703  &  --  & $0.46 \pm 0.23$ & -- & $0.14\pm0.53$  & $0.05\pm0.17$  \\
990712  &  $3.57 \pm 0.41$ & $0.43 \pm 0.11$ & $0.55 \pm 0.03$  & $0.50 \pm 0.15$  &  $0.18\pm0.01$  \\
020405  &  --  &  $0.35\pm0.10$  &  --  &  $1.93\pm0.36$  &  $0.62\pm0.12$  \\
020903  &  $3.03\pm0.91$  & $0.46\pm0.32$  & $0.15\pm0.09$  &  $0.10\pm0.57$  & $0.05\pm0.03$\\
030329  & $3.16\pm0.57$ & $0.45\pm0.12$ & $0.24\pm0.05$ & $0.25\pm0.20$ &  $0.08\pm0.02$  \\
031203  & $3.20\pm1.79$ & $0.44\pm0.25$ & $0.28\pm0.04$ & $0.40\pm0.12$ &  $0.09\pm0.01$  \\
060218  & $2.86\pm1.64$ & $0.46\pm0.34$  & $0.00\pm0.02$ & $0.10\pm0.12$  &  $0.00\pm0.01$ \\
060505\tablefootmark{a} & $3.54\pm3.59$ & $0.43\pm0.72$ & $0.53\pm0.08$  &  $0.63\pm0.35$ & $0.17\pm0.03$  \\
060505\tablefootmark{b}  &  $5.46\pm4.51$ & -- & $1.60\pm0.31$ & -- & $0.52\pm0.10$ \\
\hline
\end{tabular}
\tablefoot{\tablefoottext{a}{GRB site.}
\tablefoottext{b}{The entire host galaxy.}}
\end{table}