In a contested matter, when testimony is excluded by a ruling of the presiding officer, the party offering the evidence shall be permitted to make an offer of proof by dictating it into the record or submitting the substance of the proposed testimony in writing, prior to the conclusion of the hearing, and such offer of proof shall be sufficient to preserve the point. The presiding officer may ask such questions of the witness as he or she deems necessary to satisfy himself or herself that the witness would testify as represented in the offer of proof. An alleged error in sustaining an objection to questions asked on cross-examination may be preserved without making an offer of proof.