Final answer:
Physical factors contributing to stress reactions include sleep loss, dehydration, and preexisting medical conditions; these elements can significantly affect the body's stress responses and overall health.
Step-by-step explanation:
One of the contributing factors to stress reactions is the physical factor, which includes a variety of physiological responses that our body uses to handle demanding situations. Looking at the options provided, sleep loss (a), dehydration (b), and preexisting medical conditions (c) are all associated with physical factors that can contribute to stress.
On the other hand, worries about others (d) is more of a psychological element rather than a physical one. Sleep loss, for instance, can impair cognitive functions and increase susceptibility to stress. Dehydration impacts physical performance and can exacerbate stress responses, while preexisting medical conditions may strain the body's ability to cope with additional stressors. Therefore, the physical factors associated with stress reactions are sleep loss, dehydration, and preexisting medical conditions.