Lines 25-29 tell us that "[medical illustrations] would be inadmissible as evidence unless a medical expert were present in the courtroom to testify to their accuracy." We can infer that medical expert's role is to provide an opinion as to the accuracy of the illustration and their opinion is necessary for an illustration to be admissible, but ultimately the judge decides whether a piece of evidence is admissible in a proceeding. Medical experts - or anyone aside from the judge for that matter - have no authority to decide what is admissible, hence (A) is incorrect. (E) correctly paraphrases the role of a medical expert described on lines 28-29.
Let me know if this makes sense and if you have any further questions.