**Core Concept:** Secretomotor nerves control the exocrine glands, specifically stimulating the secretion of their respective substances. The submandibular gland is an exocrine gland in the neck.

**Why the Correct Answer is Right:** The submandibular gland is primarily secretomotor to the saliva. The saliva consists mainly of water, electrolytes, and enzymes essential for digestion and oral defense against pathogens. The correct answer is "A," as it refers to a parasympathetic nerve, which is responsible for the secretomotor function of the submandibular gland.

**Why Each Wrong Option is Incorrect:**

A. Parasympathetic - This is the correct answer, as the parasympathetic nervous system controls the salivary glands, including the submandibular gland.

B. Sympathetic - Sympathetic nerves are involved in the stress response and have no direct connection with salivary gland secretomotor function.

C. Sensory - Sensory nerves are responsible for transmitting sensory information, not controlling gland secretion.

D. Motor - Motor nerves primarily control muscle movement, not gland secretion.

**Clinical Pearl / High-Yield Fact:** The submandibular gland, along with the parotid and sublingual glands, forms the major salivary glands in the oral cavity. The parasympathetic nervous system, specifically the vagus and accessory nerves, control the secretion of these glands. A disruption or dysfunction of these nerves can lead to salivary gland disorders and xerostomia (dry mouth).

**Correct Answer:** D (Motor)