What is TRUE when serving a group of guests with a designated driver?

As a host or bartender, you have a legal responsibility to serve alcohol responsibly. This means that you cannot serve alcohol to someone who is already intoxicated, or who is visibly impaired.
Even if a guest has a designated driver, you are still responsible for ensuring that they do not overindulge. If you see a guest who is becoming intoxicated, you should stop serving them alcohol. You should also offer them non-alcoholic beverages and food.