Quarried from a site over five miles away, scientists are still puzzled as to how the prehistoric Britons managed to transport the massive stone blocks of Stonehenge over such a great distance without machinery.
A-scientists are still puzzled as to how the prehistoric Britons managed to transport the massive stone blocks of Stonehenge over such a great distance without machinery.
B- the massive stone blocks of Stonehenge are still puzzling to scientists because of how the ancient Britons managed to transport them over such a great distance without machinery.
C-scientists are still puzzled by how the prehistoric Britons managed the transportation of the massive stone blocks of Stonehenge without machinery over such a great distance.
D-the massive stone blocks of Stonehenge still puzzle scientists, who wonder how the prehistoric Britons managed to transport them over such a great distance without machinery
E-the massive stone blocks of Stonehenge are still a puzzle to scientists due to being transported over such a great distance without machinery.
The answer to the question is D.
D-the massive stone blocks of Stonehenge still puzzle scientists, who wonder how the prehistoric Britons managed to transport them over such a great distance without machinery.
To me, "them" seems to be an ambiguous pronoun. Can potentially refer to the stone blocks or to the scientists?
The other choices are not pretty, but I leaned more towards B, because the sentence had no pronoun ambiguity and the subject of the modifier comes right after the modifier.