Final answer:
A double solid line on the road signifies that it is illegal to pass in either direction, and violating this rule can result in fines.
Step-by-step explanation:
The road marking that indicates it is illegal to pass in either direction is option d, double solid line. A double solid line is used to indicate a no passing zone. It prohibits drivers from passing other vehicles in either direction, and they must wait until the line becomes broken before attempting to pass. This marking represents a clear instruction that vehicles traveling in either direction must not pass. Crossing a double solid line is considered a traffic violation and can lead to a ticket or fines, as it is supposed to represent a road condition where passing is unsafe.