T-13:tit for tat 以牙还牙
A:Why didn't you invite her to your birthday party?
A:你为什么没邀请她参加生日晚会?
B:Because she didn't invite me to hers. It is just tit for tat.
B:因为她没邀请我参加她的生日晚会,这是以牙还牙。
A:Why do you take it so seriously?
A:这又何必呢。