Answer: b) Diathesis-stress
The diathesis-stress model of depression posits that individuals who have a predisposition or vulnerability to depression (called the diathesis) are more likely to develop depression when exposed to stressors or negative life events. The study you described followed a group of adolescents over a period of time and found that those who had a higher tendency to ruminate (which could be considered a diathesis for depression) experienced more interpersonal stressors over time. This finding is consistent with the diathesis-stress model of depression, as it suggests that the adolescents who had a predisposition to ruminate were more vulnerable to the negative effects of stressors. The other models you listed (stress generation, differential sensitivity, and reward mediation) do not focus on the role of predisposition and stress in the development of depression.