Environmental immigration refers to various population migration behaviors caused by the sudden or gradual adverse impact of the natural environment and human settlement environment of human existence, including voluntary, involuntary, forced afterward, pre-planned, temporary , Permanent, individual and family-sponsored, government-led types of immigration. According to the above definitions, which of the following is not classified as environmental resettlement? ['The collective evacuation of residents of the Chernobyl nuclear-contaminated area.', 'Restricting ecological migration after grazing in order to protect the Sanjiangyuan area.', 'People in the Central Plains moved south during the Anshi Rebellion.', 'A large number of herders moved south after the capital of the Yuan Dynasty.']