**Core Concept**
Calculus, also known as sialolithiasis, is a condition characterized by the formation of stones or calculi within the salivary glands. This condition is often caused by the accumulation of calcium salts and other minerals in the gland's ducts.

**Why the Correct Answer is Right**
The parotid gland is the most common site for calculus formation, accounting for approximately 80% of all cases. This is due to the parotid gland's unique anatomy, with a longer and narrower duct that increases the likelihood of stone formation. The parotid gland's duct, also known as Stenson's duct, is more prone to obstruction and stone formation due to its longer length and smaller diameter.

**Why Each Wrong Option is Incorrect**
**Option A:** The submandibular gland is a common site for calculus formation, but it is not the most common site. The submandibular gland's duct is also prone to stone formation, but it is less common than the parotid gland.
**Option B:** The minor salivary glands are not typically associated with calculus formation, as they have a more complex and branching duct system that reduces the likelihood of stone formation.
**Option C:** The sublingual gland is not commonly associated with calculus formation, as it has a shorter and wider duct that reduces the likelihood of stone formation.

**Clinical Pearl / High-Yield Fact**
The most common symptom of calculus in the salivary gland is pain, which can be severe and radiate to the ear or face. Patients may also experience swelling and tenderness in the affected gland.

**Correct Answer: A. The parotid gland.**