N/C vs. N/O abundances (in numbers) for the MS stars (stars with log g> 3.20) in the LMC open clusters N 11 and NGC 2004 from observations by Hunter et al. (2009). The open symbols represent the stars given in Table 1. The blue shaded area indicates the domain predicted by the models by Brott et al. (2011) of Fig. 6. The initial N/C and N/O ratios are 0.141 and 0.035, respectively, as given in Sect. 3.2. The error bars on the observed N/C ratios are indicated. The error bars on the N/O ratios are of the same order of magnitude.