1. You have been in car accident. 2. You were in a car accident. 3. You did have a car accident. 4. You had a car accident. 5. You have had a car accident.
(1) and (5) are pretty similar and are used when the effects of the car accident are still apparent. (2) and (4) are pretty similar and may refer to any accident, at any time in the past. However, because the add