Dropdown Dynamic Items

Hello,

I like to create a set of Dropdown fields having the same item lists. But once I select "Item A" in the first Dropdown the rest of them will show all items except "Item A" in their list. Likewise if I select "Item B" is the second Dropdown, the rest should show all items except "Item A" and "ItemB". This way the loop should go on to the last Dropdown which would have only one item (left to select) to show.

This process should work as per order of the Dropdown Fields. Each Dropdown must have a item of blank selection (Null Value). The next Dropdown would only unlock if a selection in made to the previous Dropdown.

Please help me with the javascript coding...

Thanks in advance.