TOEFL Reading: ETS-TOEFL阅读机经 - 3662N475318398U5L$

In paragraph 3, why does the author discuss the natural decay of the wooden structures built in eighth-century Japan? A. To argue that the necessity of replacing buildings every two decades applied to all eighth-century structures, not just residences. B. To argue that the custom of residential mobility was not unreasonable given the building practices of the eighth century C. To explain why the elite of the eighth century had to move periodically to new residences D. To explain why in the sixth and seventh centuries Japanese architectural practice changed to the construction of more permanent structures