I'd focus on PT 70 onward with a few older tests if you have time (50, 51, 62, 66, 68, 69 all come to mind). The older PTs aren't worth using because they're just so different (different LR, easier RC, LG with very weird games)
For this one we want to support the conclusion "Therefore, it is advisable for businesses to implement [minor variations into its operating system software]."
Whatever AC we pick is going to either make introducing the variations sound like ...