"Lao Liu" is the screen name of Mo Mingyong, a doctoral student in Tsinghua University. When she was a graduate student in Tsinghua, she registered as a takeaway rider and delivered it for a while. In the process of sending, I have accumulated some life experiences, and there are many stories worth sharing in my study and life in Tsinghua. So the identity of "Lao Liu" is actually a doctoral student in Tsinghua University.