get all options from dropdown

[FilMar]

I have a form with a dropdown (dbjoin) and 2 cascading dropdowns.

one of those is rendered as checkbox list (multiselect)

In the php plugin (OnBeforeProcess) I get the selected data via

$ll = $formModel->getElementData('___ll_id');

it givese me something like: array ( 1 => '67', 2 => '94', 4 => '57' )

How do I get an array with all the options?

Many thanks in advance,

Filip