请帮助设置安装 php7.0 和相关软件包的首选项（其中一些不是稳定版本）。
我有操作系统 Debian 8。
我在以下位置设置包的源列表etc\apt\sources.list.d\：
security.list
deb http://security.debian.org/ stable/updates main contrib non-free
deb http://security.debian.org/ testing/updates main contrib non-free
stable.list
deb http://ftp.de.debian.org/debian/ stable main contrib non-free
deb-src http://ftp.de.debian.org/debian/ stable main contrib non-free
testing.list
deb http://ftp.de.debian.org/debian/ testing main contrib non-free
deb-src http://ftp.de.debian.org/debian/ testing main contrib non-free
unstable.list
deb http://ftp.de.debian.org/debian/ unstable main contrib non-free
deb-src http://ftp.de.debian.org/debian/ unstable main contrib non-free
我在以下位置为包设置了一些首选项文件etc\apt\preferences.d\：
security.pref
Package: *
Pin: release l=Debian-Security
Pin-Priority: 1000
stable.pref
Package: *
Pin: release a=stable
Pin-Priority: 900
testing.pref
Package: *
Pin: release a=testing
Pin-Priority: 750
unstable.pref
Package: *
Pin: release a=unstable
Pin-Priority: 50
我创建99default-release了etc\apt\apt.conf.d\包含内容的文件：
APT::Default-Release "stable";
最后，当我运行安装 php7.0 的命令时，出现下一个错误：
root@machie:/etc# apt-get install php7.0
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:
php7.0 : Depends: libapache2-mod-php7.0 but it is not going to be installed or
php7.0-fpm but it is not going to be installed or
php7.0-cgi but it is not going to be installed
W: No priority (or zero) specified for pin
E: Unable to correct problems, you have held broken packages.
PS 没有来源、首选项和 apt.conf 文件 php7.0 安装成功表单“ deb http://packages.dotdeb.org jessie all” repo。但我希望这是可能的设置偏好。
