When fat is present in the stomach,the secretion of gastrin is inhibited. This inhibition is due to:

Which hormone stimulates the stomach to secrete gastric juice?

How are the activities of the gastrointestinal tract regulated?

Which of the following enzymes is optimally active at an acidic $pH$?

Trypsinogen is converted into trypsin by . . . . . . .

Identify the type of gastrointestinal hormone based on the functions given below:
$I.$ Stimulates the crypts of Lieberkuhn
$II.$ Inhibits the secretion of glucagon by alpha cells
$III.$ Stimulates Brunner's glands to release mucus
Choose the correct option accordingly.