单选题 With the purchasing power of many middle-class households _________ behind the cost of living, there was an urgent demand for credit.
【正确答案】 D
【答案解析】本题考查动词与介词（behind）的搭配。A留下；B杠杆；C缺乏；D落后。句子的意思是：许多中产阶级家庭购买力落后于生活成本，信贷要求变得迫切。