**Core Concept**
Froment's Sign is a clinical test used to assess the function of the **ulnar nerve**, specifically the strength of the **adductor pollicis muscle**. It is an important diagnostic tool in evaluating patients with suspected ulnar nerve lesions or damage. The sign is indicative of ulnar nerve dysfunction when positive.

**Why the Correct Answer is Right**
The correct answer is related to the **ulnar nerve** and its function in the hand, particularly in the movement and sensation of the little finger and the adductor pollicis muscle. Froment's Sign is positive when a patient, due to weakness of the adductor pollicis, compensates by using the **flexor pollicis longus** (innervated by the **anterior interosseous branch of the median nerve**) to adduct the thumb, indicating ulnar nerve damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not directly relate to the primary nerve or muscle group tested by Froment's Sign.
**Option B:** Similarly, this choice is not relevant to the specific nerve function assessed by the sign.
**Option C:** This option is also incorrect as it does not correspond to the clinical application of Froment's Sign.

**Clinical Pearl / High-Yield Fact**
Froment's Sign is a crucial diagnostic tool for identifying ulnar nerve lesions, which can result from various causes including trauma, compression, or disease processes affecting the nerve. Recognizing this sign can aid in the early diagnosis and management of ulnar nerve dysfunction.

**Correct Answer:** D. Ulnar Nerve Lesion.