set obligation answer based on what a user select - by: tboy

Hello..again..
I've got two different dropdown menu.
Those objects are not set as "obliged", because I want that the user decide which one contain the value he/she prefer... I want to deny the user to proceed with the survey unless he/she had select a value from a dropdown.
After that, I would like also that, when the user select a value from the dropdown1 (or dropmenu2) , the dropdown2 (or dropmenu1) will be automatically set to "please select" ... or something similar..

Thank you very much