Answer: The correct option is b.
Step-by-step explanation:
In the given problem, the city is using sand trucks to place sand in the road during icy conditions.
Sand is used during icy condition. As it increases the friction by increasing the roughness. It can help in preventing an accident in icy condition.
The grains of the sand scrub the surface of the ice.
Therefore, the use of sand increases friction by increasing roughness.