无法在ubuntu 16.04上安装Qgis

Question

安装qgis时遇到依赖问题:我正在ubuntu 16.04上安装qgis 2.14

sudo apt-get install qgis python-qgis qgis-plugin-grass
Reading package lists... Done
Building dependency tree       
Reading state information... Done
python-qgis is already the newest version (1:2.18.9+24xenial).
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:
 qgis : Depends: python-qgis (= 1:2.14.15+24xenial) but 1:2.18.9+24xenial is to be installed
        Depends: qgis-providers (= 1:2.14.15+24xenial) but 1:2.18.9+24xenial is to be installed
        Depends: qgis-common (= 1:2.14.15+24xenial) but 1:2.18.9+24xenial is to be installed
        Recommends: qgis-plugin-globe but it is not going to be installed
 qgis-plugin-grass : Depends: qgis-plugin-grass-common (= 1:2.14.15+24xenial) but 1:2.18.9+24xenial is to be installed
                     Depends: qgis-provider-grass (= 1:2.14.15+24xenial) but 1:2.18.9+24xenial is to be installed
E: Unable to correct problems, you have held broken packages.