The correct option is A Trypsinogen to trypsin
Enzymes are often produced in inactive forms called proenzymes. e.g. trypsinogen, pepsinogen, etc. Proenzymes are converted into active forms under specific conditions. For example, pepsinogen to pepsin and trypsinogen to trypsin. One of the important factors involved in the activation of trypsinogen to trypsin is enterokinase.