(RA) are answers to the lead question. Their job is to explain the
evidence and to remain consistent with the resources you will make
Depending on how you’ve framed the investigation, the rival answers might take the form of causes (Charlie has a cavity), or characterisations of circumstances (there’s an exam at school and Charlie is not prepared). This is not an exhaustive list of the role of rival answers, but they share one common feature: they explain.
Here we create a structure in which we can evaluate the fitness of alternative explanations all at once, which allows us to assess which among them is the best explanation. Of course, this relies on your judgement, and the point of introducing this structure is to make your judgements clearer to others, and to show what you have considered when making your judgements.
Note that the quality of an explanation is often a product of a contrast with other explanations, which is a good reason to systematically represent rival answers. Why won’t the light turn on? It could be that the switch isn’t wired. It could be that the filament in the bulb is broken. Under most ordinary circumstances, a blown bulb will be the answer, but this alternative might give us pause if we know the room was recently rewired. (At the same time this demonstrates the value of Explanatory Resources.)