谁说的？

https://www.uscis.gov/green-card/after-green-card-granted/international-travel-permanent-resident

A general guide used is whether you have been absent from the United States for more than a year.

Abandonment may be found to occur in trips of less than a year where it is believed you did not intend to make the United States your permanent residence. 

While brief trips abroad generally are not problematic, the officer may consider criteria such as
whether your intention was to visit abroad only temporarily,
whether you maintained U.S. family and community ties, maintained U.S employment, filed U.S. income taxes as a resident, or otherwise established your intention to return to the United States as your permanent home.

Other factors that may be considered include whether you maintained a U.S. mailing address, kept U.S. bank accounts and a valid U.S. driver’s license, own property or run a business in the United States, or any other evidence that supports the temporary nature of your absence.