**Core Concept**
The primary action of the inferior oblique muscle is to rotate the eyeball, with a secondary effect on elevation. This muscle plays a crucial role in adduction, abduction, and elevation of the globe, particularly when the eye is in a primary position.

**Why the Correct Answer is Right**
The inferior oblique muscle originates from the anterior part of the orbital surface of the maxilla and inserts into the sclera of the eyeball. When it contracts, it produces a primary action of extorsion (outward rotation) and a secondary action of elevation. This muscle is responsible for the upward and outward movement of the eyeball, especially when the eye is in a primary position. The inferior oblique muscle also helps in adduction and abduction of the eyeball due to its anatomical position and attachment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary action of the inferior oblique muscle.

**Option B:** This option is incorrect because it is a secondary action of the inferior oblique muscle, not the primary action.

**Option D:** This option is incorrect because it is a primary action of the superior oblique muscle, not the inferior oblique muscle.

**Clinical Pearl / High-Yield Fact**
The inferior oblique muscle is often weakened or paralyzed in cases of superior oblique palsy, leading to difficulties in upward and outward gaze. This can be a key clinical finding in patients with neuro-ophthalmological disorders.

**Correct Answer: C. Extorsion**