Which of the following is a behavioral sign of stress?

Poor concentration is indeed a behavioral sign of stress. When an individual is under stress, their ability to focus and maintain attention can become compromised. This is often due to the overwhelming nature of stressors that can lead to anxiety and distraction, making it challenging to engage in tasks that require sustained cognitive effort. Stress may also activate the body's fight-or-flight response, affecting cognitive functions and leading to difficulty in processing information and making decisions.

In contrast, increased productivity and positive interactions alongside enhanced memory are typically not associated with stress. Increased productivity usually indicates effective coping mechanisms or motivation rather than stress. Positive interactions suggest healthy communication and emotional well-being, which are generally indicators of lower stress levels. Enhanced memory is often tied to positive or neutral emotional states rather than the impairing effects of stress.