**Core Concept**
Obsessive-Compulsive Disorder (OCD) is a chronic mental health condition characterized by recurring, intrusive thoughts (obsessions) that trigger repetitive behaviors (compulsions). This cycle of obsessions and compulsions significantly interferes with daily functioning and causes distress.

**Why the Correct Answer is Right**
The pathophysiology of OCD involves dysregulation of the cortico-striatal-thalamo-cortical (CSTC) circuit, particularly the orbitofrontal cortex, anterior cingulate cortex, and basal ganglia. This leads to excessive activation of the brain's reward system and decreased activity in the prefrontal cortex, resulting in the characteristic obsessions and compulsions. The serotonin system, particularly the 5-HT1A and 5-HT2A receptors, plays a crucial role in regulating the CSTC circuit and is often targeted by pharmacological interventions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the core features of OCD. While anxiety is a common comorbidity, it is not a defining characteristic of the disorder.
* **Option B:** This option is incorrect because it is too broad and does not specifically describe the repetitive behaviors and intrusive thoughts that are hallmark symptoms of OCD.
* **Option C:** This option is incorrect because it is a characteristic of other psychiatric conditions, such as schizophrenia or bipolar disorder, rather than OCD specifically.

**Clinical Pearl / High-Yield Fact**
The "Y-BOCS" (Yale-Brown Obsessive Compulsive Scale) is a widely used rating scale to assess the severity of OCD symptoms, which includes both obsessions and compulsions. It is essential for clinicians to accurately diagnose and monitor OCD using this scale to guide treatment decisions.

**Correct Answer: C. Involuntary, recurrent thoughts (obsessions) that trigger repetitive behaviors (compulsions).**