Darius conducted an observational study to learn how a successful career affects happiness. he surveyed 600 people in his hometown and found that 75% say the more success they have in their career, the more happiness they experience. choose from the following the conclusion that darius can draw from his study.

a.) a successful career is the only factor that contributes to happiness.
b.) a successful career results in happiness.
c.) happiness results in a successful career.
d.) there may be a link between a successful career and happiness.