In establishing an effective and efficent proces control system, which of the following represents the best strategy for implementing control charts $($SPC charts$)$ if the goal is to chart and control the process upstream, at the point of a greatest leverage and closest to the source of process variability?A$.$ Chart the significant process inputs variables $($XS$)$B$.$ Chart all measureable process variablesC. Chart the error rate of the processD. Chart process equipment checklist results