Explanation: Hongyan of migratory birds each year in late autumn return flight, which began when the frost, due to the timing of the change and refers to the replacement of age.
Geese as migratory birds return each autumn fly began to frost the time, as used to refer to temporal changes and the replacement of age
Geese as migratory birds return each autumn fly began to frost the time, as used to refer to temporal changes and age of the replacement. Qing Pu, "and Zhang Li You Book": "Hongfei frost, I do not know several times, cloud tree thinking, without forgetting the date."