**Core Concept**
The tensor of the vocal cord is a muscle that plays a crucial role in regulating the tension of the vocal cords during speech and respiration. It is a unique muscle in the larynx that is responsible for adjusting the length and tension of the vocal cords, thereby influencing pitch and voice quality.

**Why the Correct Answer is Right**
The tensor of the vocal cord is supplied by the external laryngeal nerve, a branch of the superior laryngeal nerve. This nerve originates from the vagus nerve (cranial nerve X) and provides motor innervation to the cricothyroid muscle, which is the tensor of the vocal cord. The cricothyroid muscle stretches and lengthens the vocal cords by tilting the thyroid cartilage forward and upward, thereby increasing tension and pitch.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct nerve supply. The recurrent laryngeal nerve, a branch of the vagus nerve, supplies all other intrinsic laryngeal muscles except the cricothyroid.
**Option B:** This option is incorrect because it does not accurately describe the nerve supply to the tensor of the vocal cord. The internal laryngeal nerve, another branch of the superior laryngeal nerve, is responsible for sensory innervation of the larynx, not motor innervation.
**Option C:** This option is incorrect because it mentions a nerve that does not exist. The superior laryngeal nerve has two branches: the internal laryngeal nerve and the external laryngeal nerve.

**Clinical Pearl / High-Yield Fact**
Remember that the tensor of the vocal cord (cricothyroid muscle) is unique in that it is the only intrinsic laryngeal muscle that is innervated by the external laryngeal nerve, a branch of the superior laryngeal nerve. This muscle plays a critical role in regulating pitch and voice quality during speech and respiration.

**Correct Answer:** C.