HII Regions And the Protosolar Helium, Carbon, and Oxygen Abundances in
  the Context of Galactic Chemical Evolution
  We present chemical evolution models of the Galactic disk with different
Z-dependent yields. We find that a moderate mass loss rate for massive stars of
solar metallicity produces an excellent fit to the observed C/H and C/O
gradients of the Galactic disk. The best model also fits: the H, He, C, and O
abundances derived from recombination lines of M17, the protosolar
abundances,and the C/O-O/H, C/Fe-Fe/H, and O/Fe-Fe/H relations derived from
solar vicinity stars. The agreement of the model with the protosolar abundances
implies that the Sun originated at a galactocentric distance similar to the one
it has. Our model for $r=3$ kpc implies that a fraction of the stars in the
direction of the bulge formed in the inner disc. We obtain a good agreement
between our model and the C/O versus O/H relationship derived from
extragalactic H~{\sc ii} regions in spiral galaxies.
