2, foil: write sadness with music. Write a sad mood with happy scenes, and set off the author's sadness with the laughter of spring flowers and the song and dance of swallows. Although the spring scenery is infinite, the country has fallen, and the poet has no intention of spring scenery, and his sadness is doubled.
3. Contrast: The smile of flowers and the dance of swallows are in sharp contrast with the author's sadness, highlighting the author's pain of national subjugation and his yearning for the motherland.