TOEFL Reading: ETS-TOEFL阅读机经 - 6L41Y1JGW661MCOVL$

According to paragraph 7, what did Renfrew conclude about the megaliths of Arran and Rousay A. Each megalith was associated with a specific agricultural community. B. Each megalith was built by between 10 and 50 people. C. Some megaliths were built using stones quarried at other places. D. Some megaliths were built gradually over time rather than all at once.