Which of the following stressors is related to unfamiliar people or pets?

The correct choice is related to the impact that unfamiliar people or pets can have on an animal's emotional state. Psychosocial stressors encompass social interactions and relationships that can induce fear or anxiety in animals. When an animal encounters unfamiliar individuals, whether human or another pet, it may experience insecurity, fear, or heightened stress due to the novel social dynamics at play. These interactions can trigger responses rooted in the animal's instinctive behaviors, leading to elevated arousal and caution.

Physiologic stressors generally refer to internal bodily changes due to stress, such as hormonal or metabolic responses. Environmental stressors pertain to the physical surroundings of the animal but do not specifically focus on the social aspect. Medical stressors relate to health issues and procedures that may cause physical discomfort or anxiety during treatment. While these categories represent significant challenges, the direct connection with unfamiliar social entities points specifically to psychosocial stressors, making it the most fitting answer.