徒劳无功; 炒冷饭; 白费口舌; 浪费精力
白费口舌；徒劳；在已经失去意义的问题上白花力气
I hate to beat a dead horse, but it is very important that you understand this before you leave.───我不想多此一举，但你离开以前必须了解这个。
Oh, Come on. Let's not beat a dead horse.───算了，别再白费口舌了。
flog a dead horse───徒劳；白费力
to flog a dead horse───徒劳无功；枉费心机
eat like a horse───吃得多
dead horse───预付的工资；旧债；无益的事
set a deadline───规定最后期限
a Trojan horse───特洛伊木马
a dead loss───绝对的损失
beat the disease───战胜疾病
dead horses───预付的工资；旧债；无益的事