当我通过 Unity 安装 Gnome 时，登录时我无法选择返回到标准 Unity 桌面。每次我尝试简单的
sudo apt-get install ubuntu-desktop
我得到错误
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
ubuntu-desktop : Depends: ubuntu-session but it is not going to be installed
Depends: unity-control-center but it is not going to be installed
Depends: unity-settings-daemon but it is not going to be installed
Recommends: xul-ext-webaccounts but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
我已经尝试了一切，但 Unity 拒绝重新安装，我不想完全重新安装 Ubuntu。我使用 Ubuntu 14.04。请帮忙！！！
