The correct option is B An enzyme converting trypsinogen into trypsin
Enterokinase is a proteolytic enzyme which is secreted from the duodenal mucosa, that changes the inactive pancreatic secretion trypsinogen into trypsin, one of the enzymes that digest proteins. It can also change inactive procarboxypeptidase into the active enzyme carboxypeptidase.
So, the correct option is option A.