Debian にカールをインストールできない

DebianにCurlをインストールしようとしていますが、残念ながら次のエラーが発生します。

The following packages have unmet dependencies: curl : Depends: libcurl3-gnutls (= 7.47.0-1) but 7.38.0-4+deb8u2 is to be installed E: Unable to correct problems, you have held broken packages.

他のスレッドが提案したように、次のようにこの問題を解決しようとしましたが、sudo apt-get autoremoveまだ同じ問題があります。

この問題をどのように解決できますか？

編集する：

出力は次のとおりですapt-cache policy。

Package files:
 100 /var/lib/dpkg/status
     release a=now
 500 http://ftp.debian.org/debian/ testing/non-free Translation-en
 500 http://ftp.debian.org/debian/ testing/main Translation-en
 500 http://ftp.debian.org/debian/ testing/contrib Translation-en
 500 http://ftp.debian.org/debian/ testing/non-free amd64 Packages
     release o=Debian,a=testing,n=stretch,l=Debian,c=non-free
     origin ftp.debian.org
 500 http://ftp.debian.org/debian/ testing/contrib amd64 Packages
     release o=Debian,a=testing,n=stretch,l=Debian,c=contrib
     origin ftp.debian.org
 500 http://ftp.debian.org/debian/ testing/main amd64 Packages
     release o=Debian,a=testing,n=stretch,l=Debian,c=main
     origin ftp.debian.org
 500 http://security.debian.org/ jessie/updates/non-free Translation-en
 500 http://security.debian.org/ jessie/updates/main Translation-en
 500 http://security.debian.org/ jessie/updates/contrib Translation-en
 500 http://security.debian.org/ jessie/updates/non-free amd64 Packages
     release v=8,o=Debian,a=stable,n=jessie,l=Debian-Security,c=non-free
     origin security.debian.org
 500 http://security.debian.org/ jessie/updates/contrib amd64 Packages
     release v=8,o=Debian,a=stable,n=jessie,l=Debian-Security,c=contrib
     origin security.debian.org
 500 http://security.debian.org/ jessie/updates/main amd64 Packages
     release v=8,o=Debian,a=stable,n=jessie,l=Debian-Security,c=main
     origin security.debian.org
 500 http://mirrors.online.net/debian/ jessie/non-free Translation-en
 500 http://mirrors.online.net/debian/ jessie/main Translation-en
 500 http://mirrors.online.net/debian/ jessie/contrib Translation-en
 500 http://mirrors.online.net/debian/ jessie/contrib amd64 Packages
     release v=8.4,o=Debian,a=stable,n=jessie,l=Debian,c=contrib
     origin mirrors.online.net
 500 http://mirrors.online.net/debian/ jessie/non-free amd64 Packages
     release v=8.4,o=Debian,a=stable,n=jessie,l=Debian,c=non-free
     origin mirrors.online.net
 500 http://mirrors.online.net/debian/ jessie/main amd64 Packages
     release v=8.4,o=Debian,a=stable,n=jessie,l=Debian,c=main
     origin mirrors.online.net
Pinned packages:
     nginx -> 1.10.0-1

内容は次のとおりです/etc/apt/sources.list。

# deb http://mirrors.online.net/debian jessie main

deb http://mirrors.online.net/debian jessie main non-free contrib
deb-src http://mirrors.online.net/debian jessie main non-free contrib

deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free

deb http://ftp.debian.org/debian/ testing main contrib non-free
deb-src http://ftp.debian.org/debian/ testing main contrib non-free