All of them. All the factors. And sometimes none of them. That is to say, it varies hugely how stutter manifests (from my perspective, at least). Sure, some cases seem to demonstrate a tendency in a particular context, but then in other similar situations, nothing happens. We should probably not worry about individual situations. We should just get used to what our stutter is, what we feel when it surfaces, and how we deal with it (how we manage it). That way, we decrease the likelihood of getting shocked by what occurs. I think.