单项选择题
Samuel H．Preston，a sociologistat the University of Pennsylvania，studied how theAmerican family is changing．He reportedthat by the time the average American couple reaches 40years of age，mey have more parents than children．This finding shows the change in lifestyles（生活方式）and duties of aging Americans．The average middle．aged couple canlook forward to caring for elderly parents some time after their own childrenhave grown up.Because Americans are living longerthan ever，more researchers andsocial workers have begun to study care giving to improve care of the elderly．When people care for an elderly relatiVe，mev often do not use community（社区）services，such as adult（成人）daycare cenVes.If the care givers are adult children，they are more likely to use such services，especially because they of ten have jobs and other business．However，the wife of anelderly person is much less likely to use support ser、7ices or to put the dependent person in a nursing home．Social workers discovered that me reason for this difference wasfear of becoming poor．An ill elderlyperson may live for years，aIld medicalcare aIld nursing homes are very expensive．An elderly couple’s savings can disappear very quickly．The other half，usually thewife，Can be left in poorliving conditions.As a resuh，she often triesto take care of her husband herself for as long as she can.
An example of changes in American lifestyles is that（）.A.theyprefer to have more children
B.meelderly like living with their children
C.themiddle-aged couples have different caregiving duties
D.theaverage age for American couples．to havechildren is 40