**Core Concept**
Recurrent oral ulcers, genital ulcers, and arthritis are classic symptoms of an autoimmune disorder that affects multiple systems in the body.

**Why the Correct Answer is Right**
The symptoms presented by the patient are characteristic of Behçet's disease, a form of vasculitis that involves the blood vessels and mucocutaneous tissues. The pathergy test, which involves pricking the skin with a sterile needle and observing for a localized reaction, is often positive in patients with Behçet's disease. The exact cause of Behçet's disease is unknown, but it is thought to be related to an abnormal immune response and the presence of certain genetic markers.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because while systemic lupus erythematosus (SLE) can cause oral ulcers, it typically does not cause genital ulcers or conjunctivitis in the absence of other symptoms. SLE is a systemic autoimmune disease that can affect multiple organs and tissues.
* **Option B:** This is incorrect because Reiter's syndrome (reactive arthritis) typically presents with conjunctivitis, urethritis, and arthritis, but not oral ulcers or genital ulcers. It is often triggered by an infection, such as chlamydia or salmonella.
* **Option C:** This is incorrect because sarcoidosis is a systemic granulomatous disease that can affect multiple organs and tissues, but it typically does not cause oral ulcers, genital ulcers, or conjunctivitis. Sarcoidosis can cause a variety of symptoms, including fatigue, weight loss, and skin lesions.

**Clinical Pearl / High-Yield Fact**
Behçet's disease is a classic example of a " vasculitis" that can affect multiple systems in the body, including the skin, mucous membranes, eyes, and joints. It is often associated with a positive pathergy test and a history of recurrent oral and genital ulcers.

**Correct Answer: C**