Since she started high school, Mark's sister Becky started spending time in the afternoon participating in afterschool clubs and going out with friends. Mark now comes home to an empty house when the school bus drops him off and he has to start dinner by himself to have it ready when his parents and sister come home, a chore he and Becky used to do together. What is the main change affecting Mark's family dynamics?
a) Parental separation
b) Becky's increased social activities
c) Financial instability
d) Changes in household chores