\begin{table}%t4
%\centering
\par
\small
\caption{The proper motions of the jet components in 3C~66A during our six epochs. \label{tab:4}} \begin{tabular}{cccccccccc}
\hline\hline
&$b_{8.4}$ &$d_{2.3}$ &$d_{8.4}$&$e_{2.3}$&$e_{8.4}$&$f_{2.3}$&$f_{8.4}$&$g_{2.3}$&$g_{8.4}$\\\hline
\noalign{\smallskip}
 $\mu\ ({\rm
mas~yr}^{-1})$&0.038~$\pm$~0.029&--0.12~$\pm$~0.10&--0.048~$\pm$~0.040&0.14~$\pm$~0.35&0.28~$\pm$~0.15&--0.10~$\pm$~0.57&0.66~$\pm$~0.16&0.60~$\pm$~1.25&--0.06~$\pm$~0.61\\ 
$\beta_{\rm app}$&1.02~$\pm$~0.78&--3.21~$\pm$~2.68&--1.28~$\pm$~1.07&3.75~$\pm$~9.37&7.50~$\pm$~4.02&--2.68~$\pm$~15.27&17.68~$\pm$~4.28&16.07~$\pm$~33.48&--1.61~$\pm$~16.34\\\hline
\end{tabular}
\end{table}