Okay, let's tackle this question about the most common major symptom of obsessive-compulsive disorder (OCD). The user provided a question with options A to D, but the options are missing. However, the correct answer is given as option C, which I assume is "Obsessions" or "Compulsions" since those are the primary symptoms. Since OCD is characterized by obsessions and compulsions, I need to figure out which one is the most common.

First, the core concept here is understanding the diagnostic criteria for OCD. The DSM-5 states that OCD involves obsessions and compulsions. Obsessions are intrusive, unwanted thoughts, while compulsions are repetitive behaviors or mental acts performed to alleviate the anxiety caused by obsessions. The most common major symptom is typically the presence of obsessions, but sometimes the question might ask about the most impairing, which could be compulsions. However, the question is about the most common, so maybe obsessions are more prevalent. Wait, actually, in many cases, people with OCD report obsessions more frequently than compulsions. Some may have only obsessions (pure O), while others have compulsions. But the question is about the "major symptom" which is part of the diagnosis. So the answer is likely obsessions or compulsions. Since the answer is option C, I need to check standard references. According to DSM-5, both are required for diagnosis, but the most common presenting symptom might be obsessions. Alternatively, maybe the question is phrased as "most common major symptom" meaning which one is more commonly reported.

In the explanation, the core concept should mention that OCD is defined by obsessions and compulsions. Then, explain that the most common major symptom is obsessions because they are the primary intrusions that drive the disorder. Compulsions are the behaviors that follow. So the correct answer is obsessions. The wrong options could be other symptoms like anxiety, depression, or other disorders like schizophrenia. But since the options aren't provided, I'll proceed with the assumption that the correct answer is obsessions. The clinical pearl might be that OCD is characterized by obsessions and compulsions, with obsessions being the most common major symptom. The correct answer is option C.

**Core Concept**
Obsessive-compulsive disorder (OCD) is defined by **recurrent, intrusive thoughts (obsessions)** and **compulsions (repetitive behaviors or mental acts)** aimed at reducing anxiety. The DSM-5 emphasizes that **obsessions** are the most common *major* symptom, often preceding compulsions in clinical presentation.

**Why the Correct Answer is Right**
Obsessions in OCD are **unwanted, ego-dystonic thoughts, images, or urges** that cause marked distress (e.g., fears of contamination, harm, or symmetry). They are **the hallmark** of OCD, driving compulsive behaviors. Neurobiologically, OCD involves hyperactivity in the orbitofrontal cortex and basal ganglia, disrupting inhibitory control. While compulsions are diagnostic, they are secondary responses to obsessions, which are more frequently reported as the primary symptom.

**Why Each Wrong Option is Incorrect**
**Option A:** *Anxiety* is a common comorbidity but not a defining feature of OCD.
**Option B:** *Depression* often co-occurs due to chronic distress but is not a

✓ Correct Answer: A. Compulsive washing of hand