Aweber web form adaption

Hi there, I have a web form with aweber that has the drop down menu with 2 options to choose from. The 2 options link to 2 separate lists, but i cannot work out how to link them to two separate page redirects. So ideally when the user selects option A, he gets signed up to list A and redirected to page A immediately. The when someone else selects option B they get signed up to list B and redirected to page B. At the moment they get signed up to the individual lists, but there is only one redirect option. I need help fast!