I believe the correct term to fill in the blank would be chronic. Lamont caring for his aging father, who suffers from dementia is a chronic stressor. This type of stress is a response to an emotional pressure that is being suffered for a very long time where the person sees that he has no control over it. From the situation, it is clear that Lamont has no choice over it, he has to take of his father no matter what the situation is. With this in the long run,, he would feel a chronic stress and it would affect or contribute to the development of illnesses such as heart or cardiovascular disorders.
