Fix the error "This system is currently not set up to build kernel modules" when Install Guest Additions CD images on VirtualBox/Ubuntu

Just install fresh-new Ubuntu 20.10 on VirtualBox 6.1, it's reported with error:

This system is currently not set up to build kernel modules.
Please install the gcc make perl packages from your distribution.

To fix it, open Terminal and enter the command:

$ sudo apt install virtualbox-guest-utils virtualbox-guest-dkms

Then Reject and Install Guest Additions CD images again.