DrOswald Conducts a Study Examining the Relationship Between the Number

Dr.Oswald conducts a study examining the relationship between the number of friends one has and the experience of daily stress and life satisfaction.She randomly samples 1,500 elderly men and women in the Memphis,Tennessee,area in the southern United States.Below are her findings.
-Life satisfaction and experience of daily stress: r = -.57 ( p = .01)
-Number of friends one has and experience of daily stress: r = .09,not sig.
-Number of friends one has and life satisfaction: r = .36 ( p = .04)

-Dr.Oswald finds that the relationship between the number of friends one has and life satisfaction is stronger for men than for women.Why might Dr.Oswald have looked for this difference?

A) To examine her study's external validity
B) To examine her study's internal validity
C) To determine whether the association was curvilinear
D) To determine whether the association was spurious