A patient shows no facial expression or emotional responsiveness.

Choice A reason: Flat affect is a severe reduction in emotional expressiveness. A patient with flat affect typically has no movement in the facial muscles, maintains a monotonous voice, and shows no change in body language regardless of the topic. This is a common negative symptom of schizophrenia and certain neurological disorders. Choice B reason: Depression is a mood disorder that can cause a blunted or sad affect, but it is not defined solely by the absence of facial expression. While depressed patients may have reduced movement, "Flat" is the precise psychiatric term for the specific objective observation of a total lack of emotional responsiveness. Choice C reason: Paranoia is a thought content disturbance involving suspiciousness or the belief that one is being targeted. While a paranoid patient might be guarded or hypervigilant, they often display intense emotional responses such as fear or anger. They do not typically present with the "flatness" or total lack of expression. Choice D reason: Anxious mood is characterized by tension, worry, and physical symptoms of arousal. An anxious patient usually shows increased facial activity, such as furrowed brows or darting eyes, which is the opposite of the immobile, non-responsive state described as a flat affect during a mental status examination.