Secretion of gastric juice is controlled by

The correct option is gastrin.

Gastric acid secretion is a highly regulated physiological process in the digestive system, controlled by both neural pathways and endocrine hormones.
When food enters the stomach, it causes distension of the stomach walls and elevates the pH. In response to these stimuli, G cells located in the antrum of the stomach secrete a peptide hormone called gastrin into the bloodstream.

Once released, gastrin stimulates the parietal cells (also known as oxyntic cells) in the gastric glands of the stomach mucosa. This stimulation prompts these parietal cells to secrete hydrochloric acid (HCl) and intrinsic factor, which are the main components of gastric juice.
Gastrin also indirectly promotes gastric juice secretion by stimulating enterochromaffin-like (ECL) cells to release histamine, which further triggers acid secretion from parietal cells.

Let's briefly look at why the other options are incorrect:
1. Cholecystokinin (CCK): This hormone is secreted by the duodenum and primarily stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder.
2. Enterogastrone: This is a hormone released by the duodenal mucosa (such as secretin or gastric inhibitory peptide) that inhibits gastric acid secretion and motility when acid or fat enters the duodenum, rather than stimulating or controlling its secretion in a positive manner.