All:

I have a Form Combo Box. There are three option inside the box for me
to select. Definitely, one option will be visible and the other two
options will be Invisible unless I click the combo box. What I am
trying to do is whenever I click the combo box and select one option
which is different from the PREVIOUS VISIBLE one, I want a simple
message of "Are you sure you want to switch the selection"?

Please advise!