\begin{table}%t2
%\centering
\par
\caption{\label{tab2}CO line ratios in the Cloverleaf.}
\begin{tabular}{cccc}
\hline\hline\noalign{\smallskip}
Line        & Integrated         & $T_{\rm b}$ ratio\tablefootmark{a}     &  Reference\tablefootmark{b}  \\
            & line flux          & to                        &        \\
            & (Jy~km~s$^{-1}$) & $^{12}$CO(3--2)           &        \\
\hline         
CO(3--2)    & $13.2\pm2.0$       & $1.00\pm0.15$	 &   1    \\
CO(4--3)    & $21.1\pm3.2$       & $0.90\pm0.13$	 &   2    \\
CO(5--4)    & $24.0\pm3.6$       & $0.65\pm0.09$	 &   2    \\
CO(6--5)    & $37.0\pm5.6$       & $0.70\pm0.10$	 &   3    \\
CO(7--6)    & $45.3\pm6.8$       & $0.63\pm0.09$	 &   3    \\
CO(8--7)    & $51.4\pm7.7$       & $0.55\pm0.08$	 &   3    \\
CO(9--8)    & $41.8\pm6.3$       & $0.35\pm0.05$	 &   3    \\
            &                    &            \\
$^{13}$CO(3--2) &$0.3\pm0.1$     & 0.025$^{+0.006}_{-0.009}$ &   4    \\[0.2mm]
           \hline
\end{tabular}
\tablefoot{\tablefoottext{a}{If all lines have the same area filling factor.
Adopted 1$\sigma$ errors are $\pm$10\% for the flux densities and $\pm$15\% for the 
brightness temperature ratios.}
\tablefoottext{b}{(1) Wei{\ss} et~al. (\cite{Weiss2003}); (2)  Barvainis et~al. (\cite{Barvainis1997}); (3) Bradford et~al. (\cite{Bradford2009}); (4) this paper.}}
\end{table}