What is the oxford comma?

Which best describes why regina tells the group, “i explained to ben that perhaps you hadn’t answered his letters because you didn’t think he was offering you enough, and that the time was getting short and you could guess how much he needed you—”? to make horace feel as though he deserves a portion of the credit to reassure ben that she was telling the truth about her motives to convince ben that he has been wise to trust what she has said to pacify horace before he gets angry about what she has done mark this and return