dropdown default value

Anyone knows how to set a default value to a dropdown component:

I have 2 DD:

with the first one I select a category and pass it as a parameter to the query realted to the 2nd drop down...

What I'd like to obtain is that in the 2nd one it shows something like :

Select article

so the user has to open the 2nd DD and select something...

[375 byte] By [gio_moria] at [2007-11-26 14:51:00]