**Core Concept**
Gastric acid secretion is regulated by a complex interplay of hormonal and nervous mechanisms. The main stimulants of gastric acid secretion are gastrin, histamine, and acetylcholine, while the main inhibitors are somatostatin, secretin, and cholecystokinin.

**Why the Correct Answer is Right**
To decrease gastric acid secretion, the body relies on the inhibitory mechanisms. Somatostatin, secretin, and cholecystokinin are the key hormones that inhibit gastric acid secretion by binding to their respective receptors on the parietal cells. Somatostatin acts through its receptors, SSTR1 and SSTR2, to decrease the release of gastrin and histamine, while secretin and cholecystokinin act through their receptors to decrease the activity of the parietal cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect as gastrin is a stimulant of gastric acid secretion, not an inhibitor.
**Option B:** This option would be incorrect as histamine is a stimulant of gastric acid secretion, not an inhibitor.
**Option C:** This option would be incorrect as acetylcholine is a stimulant of gastric acid secretion, not an inhibitor.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the main stimulants and inhibitors of gastric acid secretion are gastrin, histamine, acetylcholine, somatostatin, secretin, and cholecystokinin. Understanding the interplay between these hormones is crucial for managing conditions like peptic ulcers and gastroesophageal reflux disease.

**Correct Answer: D. Somatostatin, secretin, and cholecystokinin decrease gastric acid secretion.**