Of the Following Predictors, Which Explains the Least Amount of Variability

Of the following predictors, which explains the least amount of variability in people's ability to experience happiness?

A) Biological factors (genetics)
B) Life circumstances, including demographic factors, socioeconomic status, and geographic location
C) Daily life, including social interactions, daily work activities, and the other things that make up one's day-to-day life
D) A and B explain equally little variability in happiness