Final answer:
A pile of stones used as a monument, tombstone, or landmark is known as a cairn. Cairns are comparatively simple structures, differing from complex Neolithic structures like menhirs, steles, and dolmens, which have more elaborate forms and often ceremonial functions. The correct option is A.
Step-by-step explanation:
A heap of stones piled up as a monument, tombstone, or landmark is commonly known as a cairn. Cairns have been used for a variety of purposes by ancient cultures and continue to serve as trail markers in modern times. They differ from other types of Neolithic stone structures such as menhirs (standing stones), steles (stone slabs), and dolmens (tomb-like structures with large stone slabs).
In Neolithic societies, megalithic monuments like Stonehenge and passage tombs were prevalent, particularly in Western Europe. These structures, built from large stones, often had astronomical alignments and ceremonial significance. A cairn, a simpler form, was typically a man-made pile of stones acting as a marker or memorial.
The famous henges, such as Stonehenge, were complex megalithic structures that demonstrated advanced construction techniques, such as post-and-lintel and mortise and tenon joints, and were surrounded by multiple graves. These were not merely piles of stones, but carefully arranged compositions with a significant degree of architectural sophistication.
Hence, Option A is correct.