Answer:
The correct answer would be option D, Small, Rectangular.
Step-by-step explanation:
Mile Markers are the marks that are usually found on the highways of any country, which tells us about the miles remaining to a certain town or city.
There are boards as well on the sides of the roads which tells us about the coming towns and cities and the miles remaining to them, but the mile markers that are asked in this question are usually small rectangular marks, made up of cement on the sides of the road. These marks are usually small and are found more often than the big boards during the journey on highways.