deb http://mirrors.ustc.edu.cn/debian buster main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian buster main contrib non-free
deb http://mirrors.ustc.edu.cn/debian-security buster/updates main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian-security buster/updates main contrib non-free
deb http://mirrors.ustc.edu.cn/debian buster-updates main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian buster-updates main contrib non-free