Final answer:
The correct action at an intersection with added signs indicating all traffic must stop is to come to a complete stop, which promotes road safety and compliance with traffic laws.
Step-by-step explanation:
When approaching an intersection with added signs indicating that all traffic must stop, the correct action to take is D) Come to a complete stop as indicated by the added signs. This ensures the safety of all road users, including drivers and pedestrians. Failing to comply with the stop signs can lead to severe consequences such as traffic violations or accidents. Traffic signals are typically installed to manage traffic flow and enhance safety, especially in areas with high vehicle speeds, pedestrian crossings, and a significant number of accidents.