我正在ignore-missing使用 apt-get 测试该选项，但它实际上不起作用：
# apt install -y --ignore-missing xfce4-terminal amule
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package amule 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 'amule' has no installation candidate
这里的正确选择是什么？