George Was Born in 1925 and Grew Up in the Years

George was born in 1925 and grew up in the years of the Great Depression. His values and ideas were largely shaped by the poverty of the depression and its effects on him and his family. Martha was born in 1953 and grew up in the relative affluence of 1950s "baby boom" America. To the extent that their ideas about life are tied to their time and culture of birth, the differences that exist between George's and Martha's attitudes and values can be largely attributed to ________ differences.

A) age
B) reference group
C) idiosyncratic
D) cohort