Panel a: equivalent width of the O VIII Lyδ line as a function of the CX emission measure for different collision velocities, calculated based on the cx model in SPEX. The background thermal component is taken from the best-fit two-temperature model for Abell 85. The observed sample-averaged equivalent width is shown by a dashed line in all panels. Panel b: model calculation of S XVI CX line flux at ~3.5 keV as a function of O VIII Lyδ equivalent width. The shadow region shows the observed flux of the unidentified 3.5 keV line in Bulbul et al. (2014). Panel c: fractional change in oxygen abundance as a function of O VIII Lyδ equivalent width. The color schemes in panels b and c are the same as in panel a.