**Core Concept:** Secretomotor fibers are nerves that control the release of saliva from the salivary glands. Submandibular ganglion is a group of neurons that relay these secretomotor fibers.

**Why the Correct Answer is Right:** The correct answer, Cervical sympathetic trunk (C2-4), carries the secretomotor fibers to the submandibular ganglion. These fibers are part of the parasympathetic nervous system, which is responsible for the secretomotor function of salivary glands.

**Why Each Wrong Option is Incorrect:**

A. **Vagus nerve (C1-12):** The vagus nerve is a part of the parasympathetic nervous system but carries fibers to the parotid gland (salivary gland) and not the submandibular gland.

B. **Trunk of the sympathetic nervous system:** The trunk of the sympathetic nervous system (T1-4) carries sympathetic fibers, not secretomotor parasympathetic fibers.

D. **Ansa cervicalis:** Ansa cervicalis is a branch of the cervical plexus which carries mixed sympathetic and parasympathetic fibers, not just the secretomotor parasympathetic fibers to the submandibular gland.

**Clinical Pearl / High-Yield Fact:** To remember the correct nerve, think "Cervical sympathetic trunk (C2-4) controls submandibular glands." This information is crucial for understanding the anatomy and function of salivary glands in clinical medicine and for identifying potential surgical risks during neck surgeries.