## Core Concept
Delirium is an acute and fluctuating disturbance in mental status, characterized by altered consciousness, disorganized thinking, and perceptual disturbances. It is often caused by medical conditions, medications, or withdrawal from substances. The diagnosis and management of delirium require an understanding of its clinical features and underlying causes.

## Why the Correct Answer is Right
The correct answer, ., implies that the statement regarding delirium is not true. Typically, delirium is associated with a disturbance in consciousness, such as reduced awareness of the environment, and a change in cognition, such as memory deficit, disorientation, or language disturbance. To determine why ., is correct, let's examine each option.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, delirium involves an alteration in consciousness, which can manifest as difficulty sustaining attention, difficulty shifting attention, or a decreased level of consciousness. So, statements about altered consciousness being a feature of delirium would be correct.
- **Option B:** Delirium often presents with disorganized thinking, which can be evidenced by rambling or incoherent speech, unclear or illogical thinking, or difficulty with problem-solving. Therefore, any statement affirming the presence of disorganized thinking in delirium would be accurate.
- **Option C:** Perceptual disturbances, such as hallucinations or delusions, are common in delirium. These can be visual, auditory, or other types of sensory misinterpretations. So, any option stating that perceptual disturbances are characteristic of delirium would be true.

## Clinical Pearl / High-Yield Fact
A key point to remember about delirium is the importance of identifying and managing its underlying causes, as treatment of the underlying cause can often lead to resolution of the delirium. The **ABCDE** bundle (Awakening and Breathing Coordination, Delirium management, Early mobility, and family-centered care) is a strategy used to prevent delirium in ICU patients.

## Correct Answer: D.