α-elements patterns: [O/Fe], [Mg/Fe], [Si/Fe], and [Ca/Fe] abundances as a function of [Fe/H] for SMC stars of this work observed with UVES (red squares) and MIKE (red triangles), together with the SMC field stars (Paper I, red small circles) and the SMC GCs (Paper II, green circles). Error bars are shown for UVES and MIKE abundances. As a reference, Gaussian KDE regressions of MW abundances built from SAGA database (Suda et al. 2008) (blue line) are reported, together with their 1σ confidence interval (blue shaded area), in the background.