**Core Concept**
Selective serotonin reuptake inhibitors (SSRIs) are a class of medications commonly used to treat various psychiatric disorders. They work by increasing the levels of serotonin in the brain, which helps to improve mood and reduce symptoms of anxiety and depression.

**Why the Correct Answer is Right**
SSRIs are a first-line treatment for several anxiety disorders, including obsessive-compulsive disorder (OCD), panic disorder, and social phobia. This is because they have been shown to be effective in reducing symptoms of anxiety and improving quality of life in patients with these conditions. SSRIs work by inhibiting the reuptake of serotonin by the presynaptic neuron, allowing more serotonin to be available for binding to postsynaptic receptors. This leads to an increase in serotonin levels in the synaptic cleft, which helps to calm the anxiety response.

**Why Each Wrong Option is Incorrect**
**Option A:** While SSRIs are a first-line treatment for OCD, they are not the only option. Other medications, such as clomipramine, may also be effective in treating OCD.
**Option B:** While SSRIs are effective in treating panic disorder, they are not the only first-line treatment. Other medications, such as benzodiazepines, may also be used to treat acute panic attacks.
**Option C:** While SSRIs are effective in treating social phobia, they are not the only first-line treatment. Other medications, such as beta blockers, may also be used to treat performance anxiety.

**Clinical Pearl / High-Yield Fact**
It's worth noting that while SSRIs are a first-line treatment for these conditions, they can take several weeks to start working and may require a trial period to determine their effectiveness.

**✓ Correct Answer: D. All**