Final answer:
The preposition 'around' is the best choice to replace 'before' in indicating the circular placement of chairs by the campers around the campfire.
Step-by-step explanation:
The preposition that would best replace 'before' to convey exactly where the campers put their chairs is around. Instead of saying 'before the campfire', we can say 'around the campfire' to indicate that the campers placed their chairs in a circle surrounding the fire.
The best preposition to replace 'before' to convey exactly where the campers put their chairs would be 'around'. This indicates that the chairs were placed in a circular formation encircling the campfire, establishing a sense of community and togetherness as they roasted marshmallows. Using 'around' accurately describes the positioning of the chair's relative to the central point of interest, which in this case is the campfire.