The existing works of ancient literature, science, and philosophy do not represent the most original work produced in ancient times. The most compelling evidence for this view is that the existing works frequently refer to other works that we no longer have. Which one of the following statements, if added to the argument, most helps to justify its conclusion? ['Subversive ideas tend to be suppressed whenever they are proposed.', 'Works that contain frequent references to other works tend to be derivative.', 'Many extant works have laudable things to say about the missing works.', 'A surprisingly large number of ancient texts have been irretrievably lost.']