(c) cholecystokinin

Explanation:

The contraction of gall bladder occurs due to hormone, cholecystokinin.

Cholecystokinin is a gastrointestinal hormone that is secreted by cells in the duodenum. Its release is stimulated by the presence of fatty acids and amino acids in the small intestine. It stimulates the release of bile into the intestine by contracting gall bladder and the secretion of pancreatic enzymes. Gastrin and secretin are polypeptide hormones. Gastrin, secreted by certain cells of the pyloric glands, stimulates secretion of gastric juice into the bloodstream and churning movement of stomach. Secretin is secreted by the mucosa of the duodenum and jejunum. It stimulates secretion of water and bicarbonates in bile and activates pancreas to secrete pancreatic juice. Enterokinase of enteropeptidase is an enzyme, secreted from dudonum's glands, called the crypts of Lieberkuhn, it converts inactive trypsinogen into active trypsin.