Evolution of surface chemical compositions of 20, 25, 30, and 35 M_⊙ models (magenta, blue, red, and black lines, respectively) with the Schwarzschild (left panel) and the Ledoux (right panel) criterion being presented as functions of log T_eff. In those models, the initial rotation speed was set to be 40% of the critical value (V_c). Observational results available in the literature for massive LMC stars are also plotted; the meanings of the symbols are the same as in Fig. 7. The chemical compositions of the LBVs (filled squares) are adopted from Lennon et al. (1993) and Mehner et al. (2017) for R 71, and from Agliozzo et al. (2019) for R 143. The N/C ratio of the cool α Cyg variable HD 271182 is adopted from Luck & Lambert (1992). Open circles are N/C and N/O ratios of blue supergiants (Ia, Iab) obtained by Hunter et al. (2009); binaries have been removed (Maeder et al. 2014).