Read the following passage and do the tasks below.

The traditional American family

The nuclear family, consisting of a mother, father, and their children, may be more an American ideal than an American reality. Of course, the so called traditional American family was always more varied than we had been led to believe, reflecting the very different racial, ethnic, class, and religious customs among different American groups, but today diversity is even more obvious.

The most recent government census statistics reveal that only about one third of all current American families fits the traditional mold of two parents and their children, and another third consists of married couples who either have no children or have none still living at home. An analysis of the remaining one third of the population reveals that about 20 percent of the total number of American households are single people, the most common descriptor being women over sixty-five years of age. A small percentage, about 3 percent of the total, consists of unmarried people who choose to live together; the rest, about 7 percent, are single parents, with at least one child.

There are several easily identifiable reasons for the growing number of single-parent households. First, the sociological phenomenon of single-parent households reflects changes in cultural attitudes toward divorce and also toward unmarried mothers. A substantial number of adults become single parents as a result of divorce. In addition, the number of children born to unmarried women who choose to keep their children and rear them by themselves has increased dramatically. Finally, there is a small percentage of single-parent families that have resulted from untimely death. Today, these varied family types are typical and, therefore, normal.

In addition, because many families live far from relatives, close friends have become a more important part of family life than ever before. The vast majority of Americans claim that they have people in their lives whom they regard as family although they are not related. A view of family that only accepts the traditional nuclear arrangement not only ignores the reality of modern American family life, but also undervalues the familial bonds created in alternatives family arrangements. Apparently, many Americans are achieving supportive relationships in family forms other than the traditional one.

1. Which of the following is the main topic of the passage?

This system of the body is __________ up of our bones.