A“stressor” is defined as
(a) a trigger that prompts a stressful reaction.
(b) the physiological reaction of the body to environmental factors.
(c) a negative emotion resulting from environmental unpleasantness.
(d) the nonspecific response of the body to any demand made on it.

The correct answer is A. A trigger that prompts a stressful reaction.

Explanation:

In psychology and related fields, a "stressor" refers to a situation, agent, stimulus, event or in general terms a trigger that leads to stress usually because the trigger represents a challenge or threat to the individual. This also implies stressors are linked to reactions such as muscle tension, fear, rapid heartbeat, etc. that are part of stress. Additionally, there are many types of stressors and this can lead to different levels of stress depending on individuals' reaction and ability to manage stress. Considering this, a "stressor" can be defined as a trigger that prompts a stressful reaction.

an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.