\begin{table}%t3 
\caption{\label{t_avabunds}Mean abundances (excluding upper limits) for each metallicity  region
given on the scale 12+$\log$[X/H]$^{1}$. Solar and \ion{H}{ii}~region abundances are given for comparison. }
\small%\centerline
{
\begin{tabular}{lccccccc}
\hline \hline\noalign{\smallskip}
Species & Solar$^2$ & \multicolumn{2}{c}{Galaxy} & \multicolumn{2}{c}{LMC} &
                                                      \multicolumn{2}{c}{SMC} \\
        &       & B-stars & \ion{H}{ii}~regions$^3$ & B-stars & \ion{H}{ii}~regions$^4$&
	                                        B-stars &  \ion{H}{ii}~regions$^4$\\
\hline\noalign{\smallskip}
Carbon$^5$     & 8.39&8.00~$\pm$~0.19 (56)&--  &7.70~$\pm$~0.19 (132)&7.81~$\pm$~0.22&7.30~$\pm$~0.28 (81)&7.20~$\pm$~0.02\\
Nitrogen$^6$   & 7.78&7.62~$\pm$~0.12 (45)&7.57~$\pm$~0.30&7.13~$\pm$~0.29 (~83)&6.92~$\pm$~0.14&7.24~$\pm$~0.31 (36)&6.56~$\pm$~0.07\\
Oxygen     & 8.66&8.63~$\pm$~0.16 (54)&8.70~$\pm$~0.30&8.34~$\pm$~0.13 (133)&8.37~$\pm$~0.09&7.99~$\pm$~0.21 (80)&8.02~$\pm$~0.04\\
Magnesium  & 7.53&7.25~$\pm$~0.17 (52)&    &7.05~$\pm$~0.14 (134)&    &6.72~$\pm$~0.18 (72)&    \\
Silicon    & 7.51&7.42~$\pm$~0.07 (56)&    &7.17~$\pm$~0.10 (135)&    &6.77~$\pm$~0.09 (88)&    \\
\hline
\end{tabular}}
\smallskip
 $^{1}$  {Values in brackets indicate the  number of
stars for which abundances were estimated.}\\
 $^{2}$ {Asplund et~al. (\cite{asp05})}.\\
 $^{3}$ {Average of solar neighbourhood regions from Shaver et~al. (\cite{sha83}).}\\
 $^{4}$ {Kurt \& Dufour (\cite{kur98}).}\\
 $^{5}$ {The carbon abundances have been corrected, see text.}\\
 $^{6}$  {Supergiants have been excluded from the mean nitrogen abundances.}  
\end{table}