Final answer:
You should stop behind the stop line, which may be marked or unmarked, when waiting at a stop sign or at a red traffic light.
Step-by-step explanation:
The sentence should be completed as follows: Stop behind the stop line, marked or unmarked, when waiting at a stop sign or red light. This ensuring driver and pedestrian safety by giving pedestrians safe times to cross intersections and preventing vehicles from speeding through without regard to the posted speed limits or traffic signals. It's important to follow traffic signals to reduce the number of accidents, which in some cases can result in serious injuries or loss of life.