Final answer:
The appropriate action when a tire goes flat is to safely pull over and either change the tire with a spare or call for roadside assistance.
Step-by-step explanation:
When a tire suddenly goes flat, the appropriate action is to safely pull over to the side of the road as soon as possible. Continuing to drive on a flat tire can damage the rim and create a dangerous situation. Once you have pulled over, you should change the flat tire with a spare tire or call for roadside assistance if you are unable to do so.