Add multiple drop down lists to ASP.NET form on-the-fly

I have an ASP.NET form with one drop-down list. I want to have a "+" sign ne开发者_如何学JAVAxt to the list to allow the user to add another drop-down to the form, and so on, up to a maximum of 15 drop-downs. Ideally, this will be handled client-side, but I would also be open to a solution that involved a form post back. What is the best approach?