Read the passage, and choose the correct answer A, B, C or D for each question.

Family types vary in different countries and among different cultures. In Western, industrialized societies, the nuclear family ranks as the most common family type. It consists of a father, a mother and their children. But nuclear families exist together with many other types of family units. In the single-parent family, for example, a mother or a father heads the family alone. A blended family is formed when a divorced or widowed parent remarries. As divorce rates have risen, the number of single-parent and blended families has increased.

In many parts of the world, parents and children live together with other family members under the same roof. These complex families usually contain several generations of family members, including grandparents, parents and children. They may also include brothers or sisters and their families, uncles, aunts and cousins. Even when relatives do not live together, they still consider themselves members of the same extended family includes grandparents, uncles, aunts and cousins.

The nuclear family ranks as the most common family type ________.