Here are the rules:
8 CFR 211.1
(a) General . Except as provided in paragraph (b)(1) of this section, each arriving alien applying for admission (or boarding the vessel or aircraft on which he or she arrives) into the United States for lawful permanent residence, or as a lawful permanent resident returning to an unrelinquished lawful permanent residence in the United States, shall present one of the following:
(1) A valid, unexpired immigrant visa;
(2) A valid, unexpired Form I-551, Permanent Resident Card, if seeking readmission after a temporary absence of less than 1 year, or in the case of a crewmember regularly serving on board a vessel or aircraft of United States registry seeking readmission after any temporary absence connected with his or her duties as a crewman;
(3) A valid, unexpired Form I-327, Permit to Reenter the United States;
(4) A valid, unexpired Form I-571, Refugee Travel Document, properly endorsed to reflect admission as a lawful permanent resident;
(5) An expired Form I-551, Permanent Resident Card, accompanied by a filing receipt issued within the previous 6 months for either a Form I-751, Petition to Remove the Conditions on Residence, or Form I-829, Petition by Entrepreneur to Remove Conditions, if seeking admission or readmission after a temporary absence of less than 1 year; (
(6) A Form I-551, whether or not expired, presented by a civilian or military employee of the United States Government who was outside the United States pursuant to official orders, or by the spouse or child of such employee who resided abroad while the employee or serviceperson was on overseas duty and who is preceding, accompanying or following to join within 4 months the employee, returning to the United States; or
(7) Form I-551, whether or not expired, or a transportation letter issued by an American consular officer, presented by an employee of the American University of Beirut, who was so employed immediately preceding travel to the United States, returning temporarily to the United States before resuming employment with the American University of Beirut, or resuming permanent residence in the United States.