Mobility of individual members and family groups tends to split up family relationships. Occasionally the movement of a family away from a situation which has been the source of conflict results in greater family organization, but on the whole, mobility is disorganizing. Individuals and families are involved in three types of mobility: movement in space, movement up or down in. social status, and the movement of ideas. These are termed respectively spatial(空间的), vertical, and ideational(概念的) mobility. A great increase in spatial mobility has gone along with improvements in rail and water transportation, the invention and use of the automobile, and the availability of airplane passenger service. Spatial mobility results in a decline in the importance of the traditional home with its emphasis on family continuity and stability. Even more important is the fact that spatial mobility permits some members of a family to come in contact with and possibly adopt attitudes, values, and ways of thinking different from those held by other family members. The presence of different attitudes, values, and ways of thinking within a family may, and often does, result in conflict and family disorganization. Potential disorganization is present in those families in which the husband, wife, and children are spatially separated over a long period, or are living together but see each other only briefly because of different work schedules. One index of the increase in vertical mobility is the great increase in the proportion of sons, and to some extent daughters, who engages in occupations other than those of the parents. An- Other index of vertical mobility is the degree of intermarriage between social classes. This occurs almost exclusively between classes which are adjacent(邻近的)to each other. Engaging in a different occupation, or intermarriage, like spatial mobility, allows one to come in contact with ways of behavior. different from those of the parental home, and tends to separate parents and their children. The increase in ideational mobility is measured by the increase in publications, such as newspapers, magazines, and books, the increase in the percentage of the population owning radios, and the increase in television sets. All these tend to introduce new ideas into the home. When individual family members are exposed to and adopt the new ideas, the tendency is for conflict to arise and for those in conflict to become psychologically separated from each other.What the passage tells us can be summarized by the statement that ______.A．potential disorganization is present in the American familyB．family disorganization is more or less the result of mobilityC．the movement of a family is one of the factors in raising its social statusD．social development results in a decline in the importance of traditional families