之前使用的18.04的镜像源，发现安装libssl-dev的时候，报错了：
$ sudo apt install libssl-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libssl-dev : Depends: libssl1.1 (= 1.1.1b-1ubuntu2.4) but 1.1.1c-1ubuntu4 is to be installed
E: Unable to correct problems, you have held broken packages.
于是更换为19.10的镜像源，首先查看19.10的代号：
$ lsb_release -c
Codename: eoan
然后sudo gedit /etc/apt/sources.list，全部替换为eoan，最终的镜像源如下：
deb http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu trusty-security main universe
执行：
sudo apt update
sudo apt upgrade