Dependent Drop Down Box with multi selection check boxes??? Help.

I need help. I am trying to create what I think would be considered a Dependent Drop Down Box with multi selection check boxes?

I have a list of training task that I want to have in a drop down list.

Once the task is selected, I want the dependent drop down list to populate with the list. I want to be able to multi select the items in the list with a checkbox.

Any help is appreciated.

FYI this is for a training check list:

I.E. Task: Traffic Stop (then) Check List: Radio Communications, Vehicle Operations, Driver Contact, etc...

Thanks, Steve