Final answer:
The answer to the question is option A, assuming it relates to a historical structure similar to Stonehenge, is 30, the number of stones in Stonehenge's sarsen circle.
Step-by-step explanation:
The correct answer is option a. 30. The Dome of the Rock, a significant architectural work, is not directly mentioned in the question, but the reference you've provided talks about its design. The Dome of the Rock in Jerusalem is known for its octagonal layout of outer walls. This question seems to be related to a structure with an outer ring of stones, perhaps something similar to the Dome of the Rock's design. However, the given information does not precisely confirm the number of pillars involved in that design.
In cases where ancient historical structures are involved, such as Stonehenge, the circle of sarsen stones—which could be described as an 'outer ring of stones'—consists of 30 standing stones. Hence, assuming the question relates to a structure like Stonehenge, the answer would be 30. Nevertheless, without more context, it is difficult to be certain, and it is recommended to refer to the specific information regarding the structure in question to determine the correct number of pillars. The Dome of the Rock features an exterior design but does not define the number of outer pillars. Without more context, the exact answer is speculative, with the recommended approach being to consult detailed references about the structure in question.