Final answer:
Jack would most likely rapidly respond to the accident if he has a low threshold for arousal, as such individuals are more sensitive to stimuli and can act swiftly in unexpected situations.
Step-by-step explanation:
In the scenario where Jack witnesses an accident involving a biker being hit by a bus, Jack would most likely rapidly respond to the accident if A) Jack has a low threshold for arousal. Individuals with a low threshold for arousal are more sensitive to environments with low levels of stimulation and are quicker to respond to new or sudden changes in their environment. This sensitiveness can drive them to act swiftly when an unexpected event, like an accident, occurs. On the other hand, a high threshold for arousal (B), being preoccupied with his thoughts (C), and a low need for affiliation (D) might delay or inhibit his immediate response.
According to the concept of diffusion of responsibility, the greater the number of bystanders, the less likely any one person is to help because the responsibility to help is spread among the group. However, a person with a low threshold for arousal may overcome this bystander effect and respond quickly due to their heightened sensitivity to environmental stimuli.