Final answer:
A vehicle should typically stop at least 20 meters behind a school bus to allow for the safe exit of children, complying with traffic safety regulations.
Step-by-step explanation:
The appropriate distance that a vehicle must maintain from a school bus to allow for the safe exit of children is typically specified by local traffic laws. In general, drivers are required to stop their vehicles at a safe distance to ensure that children can enter and exit the school bus safely.
This distance varies by jurisdiction, but a common requirement is to stop at least 20 meters behind a school bus that has its stop arm extended and red lights flashing. Answer B (At least 20 meters behind) is likely the correct answer, providing enough space for children to exit the bus and cross the road if necessary. It's important that all drivers adhere strictly to these regulations to ensure the safety of schoolchildren.