Hi, I would start with what we are trying to weaken. We are weakening the idea that these ratings of on time percentage are a good measure of the efficacy of the airline staff.
The easiest way to show that this is a flawed metric is that something else is causing lateness unrelated to airline staff. perhaps one airline has older planes that break more often, or is more impacted by bad weather or some other cause of lateness.
B fits into this perfectly. Hawaiian airlines may be always on time since the weather there is always calm, and British airlines may be late often because the weather there is almost never good. This doesn't show that British has lousy staff, because it is entirely possible that the weather is the cause of the difference in timeliness.
C eliminates another alternative cause. Perhaps one airline only flies out of busy airports that have more delays, and another only flies out of calm airports with no delays. This would be another cause. However, C eliminates this as a potential cause of the differential, and thus strengthens the argument.
