Final answer:
Motorcyclists should switch from staggered formations to single file lines when entering or leaving a freeway, and during curves and turns for enhanced safety.
Step-by-step explanation:
Staggered formations of motorcyclists are appropriate on open areas of the road for visibility and safety reasons. However, they should switch to a single file line when entering or exiting freeways, as well as during curves and turns. This is because a single file line reduces the risks associated with group riding in situations where road space is constrained or when maneuverability is critical.
Option B, 'The motorcyclists are about to enter or leave a freeway, and also during curves and turns in the road.' is the correct scenario when a single line formation is advised. In such driving conditions, it's essential for motorcyclists to adopt a more defensive riding position to respond effectively to any sudden changes in the traffic flow or road conditions.