**Core Concept:** Ectopic salivary gland tumours are abnormal growths that occur outside their typical anatomical locations. Salivary glands are part of the exocrine system and play a crucial role in maintaining oral health. These tumours can be benign or malignant and can have significant effects on the surrounding structures.

**Why the Correct Answer is Right:** The correct answer, **D**, refers to the parotid gland, which is the largest salivary gland located in the face, just below the ear and in front of the mandible. The parotid gland is the most common site for ectopic salivary gland tumours due to its large size and increased exposure to external factors like trauma and infections.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** Submandibular gland is another salivary gland, but the correct answer is D (parotid gland) because submandibular glands are located deeper and are more commonly affected by sialolithiasis (stone formation) than tumours.

B. **Option B:** Sublingual gland is a salivary gland, but the correct answer is D (parotid gland) because sublingual glands are smaller and less exposed to external factors, making parotid glands a more frequent site for ectopic salivary gland tumours.

C. **Option C:** The lingual (tongue) gland is an ectodermal gland, not a salivary gland. Salivary glands are mesodermal in origin and are not present on the tongue.

**Clinical Pearl:** Salivary gland tumours can be challenging to diagnose due to their rarity, and clinical suspicion, imaging, and biopsy are essential for accurate diagnosis. Early detection and treatment can improve patient outcomes.