问题：
[D]headquartered考点:状语
答案：
解析:原句___enough, firms’ investment and R&D intensity were correlated with the happiness of area in which they were ___,分解定语从句得到主语是they,谓语是were,状语是in the area。根据语义:公司坐落于某个区域,所以选择[D]。[A]advertised打广告,[B]divided划分,[C]overtaxed课税过重,均不能选。