Data validation on combobox in userform

Hi again guys, I need some help with data validation on my comboboxes in my userforms.

I'd like it to work so that my comboboxes are validated and that no other information but the lists provided can be entered into the boxes.

Also, is there a way to get the "Begin" button on Sheet1 to recognize the last used UserForm? This is only if they need to stop the timer for whatever reason and have to get off the UserForms to do so. I'd like them to be able to return to their last used UserForm.