This appeal arises from the condemnation by the United States of approximately 320.-46 acres of land in northern Arkansas for inclusion in the Buffalo National River. The matter was referred to a three-member commission for the taking of testimony and the making of recommended findings, pursuant to Fed.R.Civ.P. 71A(h). The landowners' two expert witnesses fixed the value of the land at $276,848 and $274,000, respectively, while the Government’s expert testified that the land taken was worth $170,625. The commissioners, in a unanimous report, recommended to the District Court that the land taken be valued at $202,000. The commissioners’ recommendation was adopted by the District Court.1

On appeal the landowners claim that the testimony of the Government’s expert witness should have been stricken because it was based on inadmissible comparable sales. They also argue that the commissioners’ report did not sufficiently explain the reasoning used to reach the result recommended, as required by United States v. Merz, 376 U.S. 192, 84 S.Ct. 639, 11 L.Ed.2d 629 (1964). Although the landowners did make their motion to strike before the commissioners, neither this objection nor their argument based on Merz was brought to the attention of the District Court before it adopted the commissioners’ recommendation. “[T]he litigants have a responsibility to assist the process ... by making their *153timely objections to the report in specific ... form .... ” United States v. Merz, supra, 376 U.S. at 199, 84 S.Ct. at 643. The questions presented were not properly preserved below, and there is nothing for us to review, absent plain error or a miscarriage of justice. No such extraordinary circumstance appears in this record, and the judgment of the District Court must therefore be

Affirmed.