我一个月前安装了 Xubuntu 16.10。现在我的系统显示我正在运行 17.04（开发分支）。
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu Zesty Zapus (development branch)
Release: 17.04
Codename: zesty
我认为我没有允许系统升级到最新的预发布版本。Ubuntu 的软件和更新也无法打开。这里：
$ software-properties-gtk
aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for Ubuntu/zesty
系统的 sources.list 显示软件包安装自雅克蒂存储库。
# deb cdrom:[Xubuntu 16.10 _Yakkety Yak_ - Release amd64 (20161012.2)]/ yakkety main multiverse restricted universe
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://in.archive.ubuntu.com/ubuntu/ yakkety main restricted
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://in.archive.ubuntu.com/ubuntu/ yakkety-updates main restricted
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://in.archive.ubuntu.com/ubuntu/ yakkety universe
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety universe
deb http://in.archive.ubuntu.com/ubuntu/ yakkety-updates universe
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://in.archive.ubuntu.com/ubuntu/ yakkety multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety multiverse
deb http://in.archive.ubuntu.com/ubuntu/ yakkety-updates multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://in.archive.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu yakkety partner
# deb-src http://archive.canonical.com/ubuntu yakkety partner
deb http://security.ubuntu.com/ubuntu yakkety-security main restricted
# deb-src http://security.ubuntu.com/ubuntu yakkety-security main restricted
deb http://security.ubuntu.com/ubuntu yakkety-security universe
# deb-src http://security.ubuntu.com/ubuntu yakkety-security universe
deb http://security.ubuntu.com/ubuntu yakkety-security multiverse
# deb-src http://security.ubuntu.com/ubuntu yakkety-security multiverse
谁能帮我解决这个问题？我不明白为什么我的系统虽然安装了 16.10，却显示 17.04。
参照 我的电脑显示我正在运行 ubuntu 17.04，以下是
apt-cache policy base-files：
base-files:
Installed: 9.6ubuntu6
Candidate: 9.6ubuntu6
Version table:
*** 9.6ubuntu6 500
500 http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu yakkety/main amd64 Packages
100 /var/lib/dpkg/status
9.6ubuntu5 500
500 http://in.archive.ubuntu.com/ubuntu yakkety/main amd64 Packages