我尝试从附加驱动程序中选择驱动程序，但无法启用它。找到本文降级 xorg。我在 /etc/apt/preferences.d 中创建了一个 pin 文件。当我尝试降级时，我得到了这个
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:
nvidia-173 : Depends: xorg-video-abi-11 but it is not installable or
xorg-video-abi-12 but it is not installable or
xorg-video-abi-13 but it is not installable or
xorg-video-abi-14 but it is not installable or
xorg-video-abi-15
E: Unable to correct problems, you have held broken packages.
有没有办法安装这个驱动程序，或者我应该使用 unity 2d 回到 12.04？