Radial velocity curves of three single-lined binaries: HII 517 (left panel), HII 2172 (=HD 282965; middle panel), and HII 2406 (right panel). The RV data of Mermilliod et al. (1992) and Torres et al. (2021) are shown by purple and black dots, respectively, while the APOGEE DR17 data (Abdurro’uf et al. 2022) and our LAMOST RVs are plotted with red squares and asterisks, respectively. The orbital solutions are superimposed with a full blue line.