Ratios of non-prompt D-meson production cross sections at $\s = 13$ and $5.02$ TeV  as a function of $\pt$. Left: comparison of measurements for $\Dzero$, $\Dplus$, and $\Ds$ mesons. Right: comparison of $\Dzero$ results with FONLL+PYTHIA 8 calculations. The vertical bars and empty boxes report the statistical and systematic uncertainties, respectively.