apt-get install 时候的错误

root@mch-desktop:/bin# apt-get 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

请问我现在缺少的这个源该在哪里有链接?

谁来帮帮我吧