How does the whole poem express the sadness and resentment contained in the zither sound?

(1) Zhuan Xu vividly rendered the feeling of hurting spring's separation in The Sound of the Zheng with willows and flowers and birds;

(2) The neck chain repeatedly imagines and asks questions, and through the images of loneliness under the lamp and empty thoughts upstairs, it shows the loneliness of missing in The Sound of the Zheng;

③ Re-imagine the end couplet, and show the feelings of friends' parting and missing in the sound of the piano through the comparison of friends from south to north.