**Core Concept**
Brachial plexus injuries can result in Horner's syndrome, a condition characterized by ptosis, miosis, and anhidrosis due to disruption of the sympathetic fibers innervating the eye. The sympathetic fibers responsible for these symptoms arise from the T1 sympathetic ganglion and travel with the carotid artery.

**Why the Correct Answer is Right**
The correct answer involves the T1 nerve root, which is responsible for the sympathetic fibers that innervate the eye. The brachial plexus is formed by the C5-T1 nerve roots, and Horner's syndrome occurs when the sympathetic fibers from the T1 nerve root are disrupted. This disruption can occur due to a brachial plexus injury, leading to the characteristic symptoms of Horner's syndrome. The sympathetic fibers from the T1 nerve root travel with the carotid artery and are responsible for the dilator pupillae muscle, which is involved in pupil dilation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the C6 nerve root is involved in the formation of the brachial plexus but is not responsible for the sympathetic fibers that innervate the eye.

**Option B:** This option is incorrect as the C7 nerve root is involved in the formation of the brachial plexus but is not responsible for the sympathetic fibers that innervate the eye.

**Option D:** This option is incorrect as the T2 nerve root is not typically involved in the formation of the brachial plexus and is not responsible for the sympathetic fibers that innervate the eye.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Horner's syndrome can occur due to disruption of the sympathetic fibers from the T1 nerve root, which can be seen in brachial plexus injuries. This can be a key clinical finding in patients with brachial plexus injuries.

**Correct Answer:** C.