在 do-release-upgrade 之后，我现在正在运行 ubuntu 12.04 LTS，如下所示
> lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04
Codename: precise
但是，我发现 /etc/apt/sources.list 中的所有条目都被注释掉了，只有一个除外。
问题：在下面显示的内容中，将旧的“清晰”替换为“精确”对我来说是否安全？
## unixteam source list
# deb http://debian.yorku.ca/ubuntu/ precise main main/debian-installer restricted restricted/debian-installer # disabled on upgrade to precise
# deb-src http://debian.yorku.ca/ubuntu/ precise main restricted # disabled on upgrade to precise
# deb http://debian.yorku.ca/ubuntu/ lucid-updates main restricted # disabled on upgrade to precise
# deb-src http://debian.yorku.ca/ubuntu/ lucid-updates main restricted # disabled on …