On April 3, 2009. This old man is Song Kecheng, the current guardian of the tomb of Yu Yunwen, the Prime Minister of the Southern Song Dynasty. He only receives a monthly fee of 40 yuan for guarding the tomb. Now, he plans to let his son, Song Jianbin, continue to follow the ancestral teachings - guarding the tomb. What is the relationship between the Song family and Prime Minister Yu? Why is the Song family so committed to guarding the tomb? Recalling Prime Minister Song Kecheng: guarding the tomb is....