[单选,材料题] The information in the first paragraph is presented mainly through

问题： [单选,材料题] The information in the first paragraph is presented mainly through 根据以下材料，回答下面的题目。The FamiIvThe structure of a family takes different forms around the world and even in the same society.The family’S form changes as it adapts to changing social and economic influences.Until recently.the most common form in North America was the nuclear family，consisting of a married couple with their minor children.The nuclear family is an independent unit.It must be prepared to fend for itself.Individual family members strongly depend on one another.There is little help from outside the family in emergencies.Elderly relatives of a nuclear family are cared for only if it is possible for the family to do so.In North America，the elderly often do not live with the family;thev live in retirement communities and nursing homes.There are many parallels between the nuclear family in industrial societies.such as North America，and of families in societies such as that of the Inuits，who live in harsh environments.The nuclear family structure is well adapted to a life of mobility.In harsh conditions，mobility allows the family to hunt for food.For North Americans，the hunt for jobs and improved social status also requires mobility.The nuclear family was not always the North American standard. In a more agrarian time，the mall nuclear family was usually part of a larger extenged family.This might have included grandparents，mother and father，brothers and sisters，uncles，aunts，and cousins. In North America today，there is a dramatic rise in the number of single.parent households.Twice as many households in the United States are headed by divorced，separated，or never。married individuals as are comprised of nuclear families.The structure of the family，not just in North America，but throughout the world，continues to change as it adapts to changing conditions.Another good title for this passage would be A . listing statisticsB . telling a storyC . pointing out similaritiesD . pointing out differences