8 CFR § 316.5 Residence in the United States. [This WHOLE excerpt is "paragraph" (c), so the remedy in (ii) applies to both (i) and (ii).]
(c) Disruption of continuity of residence —(1) Absence from the United States —(i) For continuous periods of between six (6) months and one (1) year. Absences from the United States for continuous periods of between six (6) months and one (1) year during the periods for which continuous residence is required under §316.2 (a)(3) and (a)(6) shall disrupt the continuity of such residence for purposes of this part unless the applicant can establish otherwise to the satisfaction of the Service. This finding remains valid even if the applicant did not apply for or otherwise request a nonresident classification for tax purposes, did not document an abandonment of lawful permanent resident status, and is still considered a lawful permanent resident under immigration laws. The types of documentation which may establish that the applicant did not disrupt the continuity of his or her residence in the United States during an extended absence include, but are not limited to, evidence that during the absence:
(A) The applicant did not terminate his or her employment in the United States;
(B) The applicant's immediate family remained in the United States;
(C) The applicant retained full access to his or her United States abode; or
(D) The applicant did not obtain employment while abroad.
(ii) For period in excess of one (1) year. Unless an applicant applies for benefits in accordance with §316.5(d), absences from the United States for a continuous period of one (1) year or more during the period for which continuous residence is required under §316.2 (a)(3) and (a)(5) shall disrupt the continuity of the applicant's residence. An applicant described in this paragraph who must satisfy a five-year statutory residence period may file an application for naturalization four years and one day following the date of the applicant's return to the United States to resume permanent residence. An applicant described in this paragraph who must satisfy a three-year statutory residence period may file an application for naturalization two years and one day following the date of the applicant's return to the United States to resume permanent residence.
(2) Claim of nonresident alien status for income tax purposes after lawful admission as a permanent resident. An applicant who is a lawfully admitted permanent resident of the United States, but who voluntarily claims nonresident alien status to qualify for special exemptions from income tax liability, or fails to file either federal or state income tax returns because he or she considers himself or herself to be a nonresident alien, raises a rebuttable presumption that the applicant has relinquished the privileges of permanent resident status in the United States. [Not likley of any concern.]
(3) Removal and return. Any departure from the United States while under an order of removal (including previously issued orders of exclusion or deportation) terminates the applicant's status as a lawful permanent resident and, therefore, disrupts the continuity of residence for purposes of this part. [Irrelevant to this situation.]
(4) Readmission after a deferred inspection or exclusion proceeding. An applicant who has been readmitted as a lawful permanent resident after a deferred inspection or by the immigration judge during exclusion proceedings shall satisfy the residence and physical presence requirements under §316.2 (a)(3), (a)(4), (a)(5), and (a)(6) in the same manner as any other applicant for naturalization. [Not likely but possible.]
