当我运行“sudo-apt-get update”时，某些文件无法下载：
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/main/binary-amd64/Packages Connection failed [IP: 91.189.88.161 80]
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-amd64/Packages Connection failed [IP: 91.189.88.161 80]
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/main/binary-amd64/Packages Connection failed [IP: 91.189.88.161 80]
更多错误信息：
W: The repository 'http://archive.ubuntu.com/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-updates Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-backports Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
我做了什么：
sudo apt-get clean
sudo rm -rf /var/lib/apt/lists/*
但问题仍然存在。
这是我的目录中的内容sources.list.d/，以防它提供有用的信息：
maarten-baert-simplescreenrecorder-xenial.list
neovim-ppa-stable-xenial.list
nodesource.list
official-package-repositories.list
vscode.list
yarn.list
我怎样才能解决这个问题？这是我在 linux mint 18 上遇到的第一个错误apt-get，Google 没有给出任何有用的结果。