Scatter plot of the carbon abundance (log ϵ_C) as a function of metallicity. The diagonal line traces the Galactic evolution of carbon with metallicity, in the absence of any in situ enhancement. The stars in this sample are indicated by blue (CEMP-s) and red (CEMP-rs) squares. CEMP stars from the literature as compiled by Yoon et al. (2016) are superimposed: CEMP-s stars are represented as blue circles, they constitute Group I, with an average C abundance as indicated by the upper dashed horizontal line. CEMP-no stars are plotted as red circles, and define Group II.