Recent data has shown that income and volunteer time are positively related. Assuming that volunteer ...

Recent data has shown that income and volunteer time are positively related. Assuming that volunteer time is included in leisure time, what could explain this observation?
A) Higher income individuals view leisure as a normal good such that the income effect dominates the substitution effect.
B) Higher income individuals view leisure as a normal good such that the substitution effect dominates the income effect.
C) Higher income individuals view leisure as an inferior good such that the income and substitution effects both increase leisure time.
D) Both A and C.