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.

Even if enterokinase is not produced,what will be the consequence?

$CCK$ (Cholecystokinin) acts on which part of the digestive system?

Secretin hormone is secreted by

Trypsinogen is an inactive enzyme of pancreatic juice. An enzyme,enterokinase,activates it. Which tissue/cell secretes this enzyme? How is it activated?