**Core Concept**
Repetitive behaviors, such as excessive handwashing, can be a manifestation of Obsessive-Compulsive Disorder (OCD), which involves unwanted, intrusive thoughts and compulsions to perform specific rituals to alleviate anxiety.

**Why the Correct Answer is Right**
The lady's behavior is characteristic of OCD due to the presence of obsessive thoughts (fear of acquiring AIDS) and compulsive behaviors (repeatedly washing her hands) aimed at reducing anxiety. In OCD, these obsessions and compulsions are typically time-consuming, interfere with daily functioning, and cause significant distress. The lady's behavior is a classic example of a "symmetry rule" or "magical thinking" – she believes that washing her hands will prevent the perceived harm (acquiring AIDS). This is a common coping mechanism in OCD, where individuals attempt to neutralize their anxiety by performing specific actions.

**Why Each Wrong Option is Incorrect**
* **Option B:** Mania, a feature of bipolar disorder, is characterized by an abnormally elevated mood, increased energy, and decreased need for sleep. It does not typically involve repetitive behaviors or obsessive thoughts.
* **Option C:** Depression is a mood disorder characterized by persistent sadness, loss of interest in activities, and changes in appetite or sleep patterns. While individuals with depression may exhibit ritualistic behaviors, these are not the primary features of the disorder.
* **Option D:** Anxiety disorders, such as generalized anxiety disorder or panic disorder, involve excessive worry or fear, but they do not typically involve the same level of repetitive, compulsive behaviors seen in OCD.

**Clinical Pearl / High-Yield Fact**
In diagnosing OCD, clinicians should be aware of the "four As": **A**dverse consequences (e.g., social isolation), **A**ssociation with other mental health conditions (e.g., depression, anxiety), **A**ffect on daily functioning, and **A**ssociation with specific rituals or compulsions.

**✓ Correct Answer: A. OCD**