问题
点击「设备」-「安装增强功能」，然后就弹出下面这个东西，
Unable to insert the virtual optical disk D:\Program\Orade\VirtualBox\VBoxGuestAdditions.iso into the machine lubuntu1810.
Could not mount the media/drive 'D:\Program\Orade\VirtualBox\VBoxGuestAdditions.iso' (VERR_PDM_MEDIA_LOCKED).
Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}
Callee: IMachine {5047460a-265d-4538-b23e-ddba5fb84976}
解决方案：
1。手动安装VBoxGuestAdditions
sudo mkdir --p /media/cdrom
sudo mount -t auto /dev/cdrom /media/cdrom/
cd /media/cdrom/
sudo sh VBoxLinuxAdditions.run
2。重启虚拟机就可以了
参考网站：
https://blog.csdn.net/qq811616536/article/details/52652903
https://askubuntu.com/questions/80341/unable-to-mount-virtualbox-guest-additions-as-a-guest-win7-host
https://jingyan.baidu.com/article/574c521917db806c8d9dc18c.html