【单选题】

What is the typicalAmerican family (21) MarriedAmerican adults will name their husband or wife and their children (22) their "immediate family"(直系家庭). If they (23) their father, mother, sisters, or brothers, they will define them as separate units, usually (24) in separate households.Aunts, uncles, cousins, and grandparents are (25) "extended family"(扩大的家庭).

The structure of theAmerican family has undergone great changes (26) the 1950s. Traditionally, theAmerican family (27) been a nuclear family, consisting (28) a husband, a wife, and their children. Grandparents (29) live in the same home with their (30) sons and daughters.
In the 1950s, 70 percent ofAmerican households (31) the "classic"American family—a husband, wife, and two children. The father earned the money to (32) the family, the mother (33) the children and did not work outside the home, and they had two children.
Yet, in the 1990s,only 8 percent ofAmerican households consisted of a (35) father, a stay-at- home mother, and two children.And (35) ,18 percent of households consisted of two parents who were both working and some or more children living at home.
26
A、since
B．before
C．ever
D．when