**Core Concept**
Gastric acid secretion is a complex process involving the parietal cells of the stomach lining. The main stimulus for gastric acid secretion is the release of histamine, gastrin, and acetylcholine, which act on the parietal cells to increase acid production. Effective ulcer treatment often targets this pathway to reduce acid secretion and promote healing.

**Why the Correct Answer is Right**
Histamine, gastrin, and acetylcholine stimulate the parietal cells to increase acid production by binding to their respective receptors. Histamine acts on H2 receptors, gastrin acts on gastrin receptors, and acetylcholine acts on muscarinic receptors. Inhibiting the action of histamine on H2 receptors is a key mechanism for reducing gastric acid secretion. Ranitidine is a well-known H2 receptor antagonist that works by competitively inhibiting histamine at the H2 receptor, thereby reducing gastric acid secretion.

**Why Each Wrong Option is Incorrect**
* **Option A:** H2 receptor antagonists like ranitidine are the correct choice, not antacids like aluminum hydroxide or magnesium hydroxide, which work by neutralizing acid rather than inhibiting its production.
* **Option B:** Proton pump inhibitors (PPIs) like omeprazole are effective in reducing acid production but work by irreversibly inhibiting the H+/K+ ATPase enzyme on the parietal cell surface, not by inhibiting histamine action.
* **Option C:** Antacids like calcium carbonate work by neutralizing stomach acid, not by inhibiting gastric acid secretion.
* **Option D:** Anticholinergics like atropine work by blocking the action of acetylcholine on muscarinic receptors, not by inhibiting histamine action.

**Clinical Pearl / High-Yield Fact**
H2 receptor antagonists like ranitidine are effective in reducing gastric acid secretion and are often used in the treatment of peptic ulcers, especially when PPIs are not tolerated or contraindicated.

**Correct Answer:** C.