问在lubuntu上安装curl (和其他软件包)有问题

EN

sudo apt install curl

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package curl is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'curl' has no installation candidate

sudo apt-get update

Get:1 http://fi.archive.ubuntu.com/ubuntu xenial InRelease [247 kB]
Hit:2 http://dl.google.com/linux/chrome/deb stable InRelease                                                                         
Hit:3 http://ppa.launchpad.net/pinta-maintainers/pinta-stable/ubuntu groovy InRelease                                                
Ign:4 http://ppa.launchpad.net/webupd8team/java/ubuntu groovy InRelease                                                              
Hit:5 https://download.mono-project.com/repo/debian stable-buster InRelease                                                          
Err:6 http://ppa.launchpad.net/webupd8team/java/ubuntu groovy Release
  404  Not Found [IP: 2001:67c:1560:8008::19 80]
Err:1 http://fi.archive.ubuntu.com/ubuntu xenial InRelease   
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/webupd8team/java/ubuntu groovy Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://fi.archive.ubuntu.com/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
E: The repository 'http://fi.archive.ubuntu.com/ubuntu xenial InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.