Research findings of marital satisfaction in the later years of long-term marriages may in part be due to the fact that

A) children have left home.
B) menopause has eliminated the fear of pregnancy.
C) older samples do not include couples that have already gotten divorced.
D) studies were longitudinal.

Older samples in research on marital satisfaction often do not include couples that have already divorced, which can skew the findings toward more positive outcomes. This is because the sample is biased towards couples who have remained married, potentially indicating higher satisfaction or other factors that contribute to a long-lasting marriage.