**Core Concept**
An abnormal attitude refers to an abnormal posture or position of the body, often resulting from neuromuscular or musculoskeletal disorders. This concept is essential in understanding various conditions affecting the nervous system, musculoskeletal system, and motor control.

**Why the Correct Answer is Right**
The correct answer choice illustrates an abnormal attitude, such as the "scissor posture" seen in patients with Parkinson's disease. This posture is characterized by a flexed posture of the knees and elbows, with the feet pointing inward. This is due to the imbalance of dopaminergic and cholinergic neurotransmission in the basal ganglia, leading to impaired motor control and rigidity.

**Why Each Wrong Option is Incorrect**
**Option A:** While a slouched posture can be considered abnormal, it does not specifically illustrate an abnormal attitude as defined by an altered position of the body parts.
**Option B:** A person standing with their feet shoulder-width apart is a normal attitude, not an abnormal one.
**Option C:** A person lying down on a bed is also a normal attitude, not an abnormal one.

**Clinical Pearl / High-Yield Fact**
The "scissor posture" in Parkinson's disease is a classic example of an abnormal attitude. Remember that abnormal attitudes can result from various conditions, including neuromuscular disorders, musculoskeletal disorders, and neurological conditions.

**Correct Answer: C. A person standing with their feet shoulder-width apart.**