The correct answer is B. Homogeneity within subgroups: High; Chance for differences between subgroups: Maximized . The CSSBB control-chart material states that subgroups are selected in a way that makes each subgroup as homogeneous as possible and that gives the maximum opportunity for variation from one subgroup to another . This is the exact principle of rational subgrouping .

The logic is central to Shewhart charting. Within a subgroup, samples should represent conditions that are as similar as possible so that the short-term, common-cause variation is captured inside the subgroup. Across subgroups, the chart should have the best chance to reveal time-to-time or lot-to-lot changes, which is why the opportunity for differences between subgroups should be maximized. The CSSBB source further explains that when product is taken as nearly as possible at one time, this gives a minimum chance for variation within a subgroup and a maximum chance for variation from subgroup to subgroup . Therefore, the verified answer is B , which exactly matches the CSSBB definition of rational subgroup selection.