Force selection from drop-down

Is there anyway to force the user to enter a selection from the drop-down? For example, if I enter in canton, the user should choose canton, ma from the drop-down. Otherwise, if they tab to the next field, they can submit it just as canton, and we don’t know which state it references.. Also, the user can enter in bogus text with random characters and numbers, without selecting an item from the drop-down, which gives us data that isn’t useful.