**Core Concept**
Obsessive-Compulsive Disorder (OCD) is characterized by the presence of obsessive thoughts and compulsive behaviors that an individual feels compelled to perform. The defence mechanism in OCD is primarily driven by the attempt to reduce anxiety and alleviate feelings of guilt or shame associated with the obsessive thoughts.

**Why the Correct Answer is Right**
The defence mechanism in OCD often involves the use of **repression**, where the individual unconsciously pushes the anxiety-provoking thoughts into the unconscious mind. This is achieved through the **cortical-striatal-thalamo-cortical (CSTC) circuit**, which is a neural network involved in the regulation of motor and cognitive functions. In OCD, the CSTC circuit is hyperactive, leading to the excessive activity of the **dorsolateral prefrontal cortex (DLPFC)**, which is responsible for executive function and decision-making. The hyperactivity of the DLPFC contributes to the development of compulsive behaviors.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the defence mechanism in OCD. While **denial** is a defence mechanism, it is not the primary defence mechanism in OCD.
**Option B:** This option is incorrect because **projection** is a defence mechanism that involves attributing one's own unacceptable thoughts or feelings to someone else. This is not a characteristic feature of OCD.
**Option C:** This option is incorrect because **rationalization** is a defence mechanism that involves creating logical explanations for unacceptable behavior. While individuals with OCD may rationalize their compulsive behaviors, this is not the primary defence mechanism at play.
**Option D:** This option is incorrect because **identification** is a defence mechanism that involves identifying with someone or something that is perceived as ideal or desirable. This is not a characteristic feature of OCD.

**Clinical Pearl / High-Yield Fact**
In individuals with OCD, the use of **selective serotonin reuptake inhibitors (SSRIs)** can help to reduce the symptoms of the disorder by increasing the levels of serotonin in the brain. SSRIs can also help to decrease the activity of the CSTC circuit and reduce the hyperactivity of the DLPFC.

**Correct Answer:** B. Projection