With the approval of the officer, a witness may read into the record, as his testimony, statements of fact or expressions of opinion prepared by the witness, or written answers to interrogatories of counsel. A prepared statement of a witness who is present at the hearing may be received as an exhibit, provided that the statement does not include argument. Before any such statement is read or admitted in evidence, the witness shall deliver to the officer, the reporter, and to opposing counsel, as may be directed by the officer, a copy of such statement or of such interrogatories and the written answers thereto. The admissibility of the evidence contained in such statement will be subject to the same rules as if such testimony was produced orally, including the right of cross-examination of the witness. The officer may require that the witness testify orally if, in the officer's opinion, the memory or demeanor of the witness may be of importance.