A member of the following classes shall be presumed to have been lawfully admitted for permanent residence even though a record of his admission cannot be found, except as otherwise provided in this section, unless he abandoned his lawful permanent resident status or subsequently lost that status by operation of law: (a)Prior to June 30, 1906. An alien who establishes that he entered the United States prior to June 30, 1906. (b)United States land borders. An alien who establishes that, while a citizen