Ubuntu 14.04.4 快照更新后，LibreOffice 被删除（&uninstallable）

在接受 Ubuntu 14.04 LTS 的最新更新后，安装了“快照”（不知道这是什么）。在建议的重新启动后，系统在没有 LibreOffice 的情况下重新启动。

按照官方推荐的路径重新安装 不起作用。代码在这里：

a@a-Aspire:~$ sudo apt-get install libreoffice
Reading package lists... Done
Building dependency tree       
Reading state information... Done
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:
 libreoffice : Depends: libreoffice-base but it is not going to be installed
               Depends: libreoffice-calc but it is not going to be installed
               Depends: libreoffice-core (= 1:4.4.2-0ubuntu1~ubuntu14.04.1~c42.ppa1) but it is not going to be installed
               Depends: libreoffice-draw but it is not going to be installed
               Depends: libreoffice-impress but it is not going to be installed
               Depends: libreoffice-math but it is not going to be installed
               Depends: libreoffice-report-builder-bin but it is not going to be installed
               Depends: libreoffice-writer but it is not going to be installed
               Depends: libreoffice-avmedia-backend-gstreamer but it is not going to be installed
               Depends: libreoffice-java-common (>= 1:4.4.2~) but it is not going to be installed
               Depends: python3-uno (>= 4.4.0~beta2) but it is not going to be installed
               Recommends: libreoffice-gnome but it is not going to be installed or
                           libreoffice-kde but it is not going to be installed
E: Unable to  correct problems, you have held broken packages.

请帮我重新安装 LibreOffice。谢谢 ：）