Why Did Scientists Originally Hypothesize That Proteolytic Enzymes Such as Pepsin

Why did scientists originally hypothesize that proteolytic enzymes such as pepsin and trypsin are secreted in inactive form?

A) These proteolytic enzymes, in active form, would digest the very tissues that synthesize them.
B) They identified the hormone that activates pepsin and trypsin.
C) The stomach is too acidic to maintain these enzymes in their active form.
D) Pepsin and trypsin have never been isolated in their fully activated form.
E) Pepsin and trypsin were discovered to have protein folding patterns different from those seen previously.