**Core Concept**
The patient's symptoms and test results suggest a conductive hearing loss on the right side, as evidenced by the negative Rinne's test and the lateralization of the Weber's test to the left ear. This indicates a problem with sound conduction in the middle ear.

**Why the Correct Answer is Right**
The patient's decreased hearing in the right ear for the last two years suggests a chronic condition. The negative Rinne's test without masking on the right ear suggests that bone conduction is better than air conduction, which is characteristic of conductive hearing loss. The Weber's test lateralizing to the left ear further supports this, as the tone is perceived as louder in the ear with normal hearing. This indicates that the sound is being conducted through the skull, bypassing the affected ear.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
In conductive hearing loss, the patient may perceive the sound as louder in the unaffected ear during the Weber's test, as the sound is being conducted through the skull. This is because the unaffected ear has normal hearing and can detect the sound more easily.

**Correct Answer:** C. Semicircular canal fistula.