\begin{table}%t3
%\centering
\par
\caption{Averaged diagnostic flux ratios.}
\label{table:3}
\begin{tabular}{l c c c}
\hline\hline
            \noalign{\smallskip}
  Sample                &  
  Number$^{{a}}$ &
  C IV / He II &
  C III] / C IV \\
            \noalign{\smallskip}
\hline
            \noalign{\smallskip}
HzRG  & 49 & $\rm 1.42^{+0.10}_{-0.09}$ & $\rm 0.67^{+0.06}_{-0.06}$ \\
            \noalign{\smallskip}
QSO2  &  6 & $\rm 2.07^{+0.36}_{-0.31}$ & $\rm 0.52^{+0.08}_{-0.07}$ \\   
            \noalign{\smallskip}
Sy2   &  8 & $\rm 2.20^{+0.16}_{-0.15}$ & $\rm 0.49^{+0.06}_{-0.05}$ \\ 
\hline
\end{tabular}
\begin{list}{}{}
\item[$^{{a}}$]  
  Number of objects for which both of the flux ratios
  of C{\sc iv}$\lambda$1549/He{\sc ii}$\lambda$1640
  and C{\sc iii}]$\lambda$1909/C{\sc iv}$\lambda$1549
  were measured. Objects with a lower-limit or
  upper-limit data are not included.
\end{list}
\end{table}