First row (top): gas-phase He mass fraction, Y_gas, as a function of the gas-phase O mass fraction, X_O,gas. Second row: Y_gas vs. X_C,gas. Third row: Y_gas vs. X_N,gas. Fourth row: Y_gas vs. X_C+N,gas. Fifth row (bottom): predictions for the radial profile of Y_gas as a function of the galactocentric distance, d, with the colour coding representing the O mass fraction. From left to right, the various columns correspond to each of our reference galaxies, from galaxy A to galaxy C, respectively.