**Core Concept**
Salivary gland tumors are a diverse group of neoplasms that arise from the epithelial cells of the salivary glands, which include the parotid, submandibular, and minor salivary glands. These tumors can be benign or malignant and vary in their clinical presentation and behavior.

**Why the Correct Answer is Right**
The majority of salivary gland tumors are benign, with approximately 70-80% being non-malignant. Among these, the parotid gland is the most common site of involvement, accounting for about 70-80% of all salivary gland tumors. Warthin tumor, a type of benign tumor, is almost always found in the parotid gland, which makes option B true. Minor salivary gland tumors, however, have a higher propensity for malignancy compared to major salivary gland tumors, but they are not mostly malignant overall. The key to answering this question lies in understanding the relative frequencies and characteristics of different types of salivary gland tumors.

**Why Each Wrong Option is Incorrect**
**Option A:** Parotid gland is most common site of involvement - This statement is true, as the parotid gland is the most common site of involvement for salivary gland tumors.
**Option B:** Warthin tumour almost always found in the parotid gland - This statement is also true, as Warthin tumor is a type of benign tumor that is predominantly found in the parotid gland.
**Option C:** Minor gland tumours are mostly malignant - While minor salivary gland tumors do have a higher propensity for malignancy, they are not mostly malignant overall. This statement is an overgeneralization.

**Clinical Pearl / High-Yield Fact**
When evaluating salivary gland tumors, it's essential to consider the patient's age, sex, and location of the tumor. For example, Warthin tumor is more common in older men, while pleomorphic adenoma is more common in women. Additionally, patients with a history of radiation exposure or familial syndromes may be at increased risk of developing salivary gland tumors.

**✓ Correct Answer: D. Parotid tumours are mostly malignant**