Getting a QueryString from a DropDownList

Question

I am using Microsoft Expression Web 3 and I have to pages, the first with a DropDownList and a button and the last shows the result. The DropDownList contains a list of countries where the user is supposed to select a country and the click on the button, this should send the user to a new page to see what's needed to travel to that country.

I am trying to use a QueryString, so that it will send the user to

.../simple_country_view.aspx?vaksinecountry_id={0}

So that if the country with the id 17 is selected, it will go to this URL

.../simple_country_view.aspx?vaksinecountry_id=17