question about dropdown-menu

question about dropdown-menu

Hi,

I've just created a simple web site (for school) where people have to make a "top-3" of the best pictures/poems.

So I've made 3 drop-down-menu's with al the options where they can choose from.

The problem is that it's possible to choose 3 times the same option.

Is it possible to adjust the drop-down-menu's so people can choose every option only once?
So they have to choose 3 different options?

I hope I've made myself clear... My English isn't very good


=> http://deurgang.freehostia.com/Stemformulier.html


Thank you in advance!