TOEFL Listening: ETS-TOEFL听力机经 - QH13P191VGU91_78P$

According to the professor, how did Wright make use of boulders at Fallingwater? A. As a structural foundation to support the house B. As steps between the floors in the house's interior C. As a way to modify the flow of the waterfall during construction D. As an interior feature serving as a reminder of the exterior landscape