When are commas necessary to include with numbers

Which is the best contrast between the heracles myth and christopher reeve's life story? a. the mythical heracles and christopher both endured many trials calling on their reserves of strength and character. b. christopher reeve was injured on a horse, but heracles fought a bear. c. heracles' journey into the dark world of the afterlife pales beside christopher reeve's real-life struggle against grief and depression. d. heracles wasn't real but christopher reeve was.