**Core Concept**
Lichen planus is a chronic inflammatory condition that affects the skin, mucous membranes, and other areas of the body. Oral manifestations of lichen planus can include various lesions and changes in the oral mucosa.

**Why the Correct Answer is Right**
The correct answer is a characteristic oral manifestation of lichen planus, known as Wickham's striae. These are thin, white lines or striations that appear on the surface of the oral mucosa, often on the buccal mucosa or the tongue. The exact cause of Wickham's striae is not well understood, but they are thought to result from the inflammatory response and the subsequent scarring that occurs in lichen planus. The presence of Wickham's striae in the oral cavity is a key diagnostic feature of lichen planus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while oral lichen planus can cause a range of symptoms, including pain and discomfort, it is not a specific type of lesion.

**Option B:** This option is incorrect because oral lichen planus is not typically characterized by a single, distinct lesion.

**Option C:** This option is incorrect because while oral lichen planus can cause changes in the oral mucosa, it is not typically associated with a "cobblestone" appearance.

**Clinical Pearl / High-Yield Fact**
One key clinical pearl to remember is that Wickham's striae are a highly specific and sensitive feature of oral lichen planus, making them a valuable diagnostic tool for clinicians.

**Correct Answer:** C.