bill@debian:~$ apt-cache policy nvidia-driver
nvidia-driver:
  Installed: (none)
  Candidate: 384.130-1
  Version table:
     390.87-2~bpo9+1 100
        100 http://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/non-free amd64 Packages
     384.130-1 500
        500 http://mirrors.tuna.tsinghua.edu.cn/debian stretch/non-free amd64 Packages