TOEFL Reading: ETS-TOEFL阅读机经 - M185ZFZ341Z808QJL$

Which of the sentences below best expresses the essential information in the highlight sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Because of favorable conditions in southern Scandinavia and the social complexity of their societies, hunter-gatherer societies did not adapt to farming until economic change required it. B. When farming came to Europe and became common, hunter-gatherer societies finally achieved high levels of social complexity. C. Social complexity was common in the societies of southern Scandinavia but was less common in other areas where farming came later. D. Hunter-gatherer societies in southern Scandinavia achieved a new level of social complexity, and this allowed them to quickly achieve economic and social change when farming was introduced.