How to know which dropdownlist onchange event was triggerd in asp.net?

How to know which dropdownlist onchange event was triggerd in asp.net?

Im trying to do a rather simple practice project and i got stuck for a
while now.
I have 3 dropdownlists and 3 views.
I want to do: check if the current dropdownlist has chosen a value then
that dropdown has a value, hide that view and show the next view.
my problem: I have one method for all 3 of my dropdownlists that gets
called when a change occurs. I need to check which one of these
dropdownlists triggerd the change so that i know which dropdownlist value
i need to check(if it is empty or not) and depending on the value i
show/hide views.
If more info is needed just ask and Thanks!