Kirong v. Mukasey, 529 F.3d 800 (8th Cir. Jun. 20, 2008) (where the record is ambiguous as to whether noncitizen intended to indicate he was a United States citizen or a National by checking "citizen or nation" box on I-9 form, noncitizen has failed to meet his burden to show clearly and beyond doubt that he is not inadmissible to the United States as a noncitizen who has made a false claim to U.S. citizenship).