In Discussing the Relative Importance of Within- and Between-Family Differences

In discussing the relative importance of within- and between-family differences, your textbook authors suggest that __________.

A) in general, within-family differences are more important than between-family differences
B) between-family differences are fairly important in the development of intelligence
C) between-family differences may be more important when we consider families from a wider range of socioeconomic classes, and from different cultures
D) all of the above