Full Screen XP installation in VirtualBox

Mssql 2005 needs to be installed, so a VirtualBox was installed on the local machine yesterday.
It is installed with XP, but today it is found that the full screen is not available.
I have found a lot of information on the Internet. Generally, I click "Install enhancement" in the "device" menu, but it won't work after I try it;
The final solution is:
Copy VBoxGuestAdditions. iso in the VirtualBox installation directory to the virtual machine, run it, and restart it;
 
PS: Windows 7

From xiaoyang0878