Answer: D. stressor
Stressors are circumstances or situations experienced by individuals capable of causing real-life changes. These situations often include traumas and life crises. Life stressors, in particular, tend to alter the body’s allostatic balance and this leads to psychological stress like anxiety and depression. Stressors are potential threats to an animal or individual. With this, the body tends to respond to the stress by adapting and creating a balance in the allostatic level of the body to reduce the effect of the stress; this is known as the stress response.