What is the typical positioning of the two turret structures associated with each milecastle on Hadrian's Wall?

A. Approximately one-third and two-thirds of a Roman mile to the west of the milecastle
B. Approximately one-quarter and three-quarters of a Roman mile to the east of the milecastle
C. At the midpoint of the Roman mile to the north and south of the milecastle
D. Immediately adjacent to the milecastle and at the Roman mile marker to the east
Answer: 