**Core Concept**
The question tests the student's knowledge of the dermatomal distribution of the spinal nerves. Specifically, it requires understanding the sensory innervation of the upper limb, which is crucial for diagnosing nerve root injuries.

**Why the Correct Answer is Right**
The C8-T1 spinal nerve roots innervate the medial aspect of the forearm and the medial aspect of the hand. The medial antebrachial cutaneous nerve, a branch of the C8-T1 spinal nerve roots, provides sensory innervation to the medial forearm. Therefore, sensory loss in the area supplied by this nerve would confirm the injury to the C8-T1 nerve roots. The medial antebrachial cutaneous nerve is responsible for sensation in the medial aspect of the forearm, from the elbow to the wrist.

**Why Each Wrong Option is Incorrect**
* **Option A:** The lower lateral brachial cutaneous nerve is not a specific nerve root derivative; it is more of a general term. It may supply some sensory fibers to the lateral forearm, but it is not directly associated with C8-T1 nerve roots.
* **Option B:** The musculocutaneous nerve is associated with the C5-C7 nerve roots, primarily providing motor innervation to the biceps brachii, brachialis, and coracobrachialis muscles. It does not have a direct sensory contribution.
* **Option C:** The intercostobrachial nerve is a branch of the T2 spinal nerve root and provides sensory innervation to the medial aspect of the arm, not the forearm or hand. This nerve is not related to the C8-T1 nerve roots.

**Clinical Pearl / High-Yield Fact**
The dermatomal distribution of the spinal nerves is essential for diagnosing nerve root injuries. Remember that the C8-T1 nerve roots are responsible for sensation in the medial aspect of the forearm and hand.

**✓ Correct Answer: D. Medial antebrachial cutaneous nerve**