Concept:A combination of high industrial and agricultural activity creates many economic opportunities and attracts dense population.Explanation:The north-east of the U.S.A. is a major industrial region with numerous manufacturing cities and commercial centres.It also possesses fertile agricultural lands that supply food and raw materials.These features generate employment and trade, drawing a large number of people to the area.The Amazon basin, Niger valley, and North Africa do not offer such a balanced mix of intense industrial and agricultural development.Answer:B. the north east of U.S.A