Duì buqĭ!

means " excuse me " when a re-
quest is being made or " sorry " as an apology for something improper, wrong or an accident that might have caused unpleasant feelings. "Hěn bàoqiàn " and " qǐng yuánliàng " are used only as an apology. So be aware of the circumstances and use " duì bùqǐ "," hěn bàoqiàn " and " qǐng yuánliàng "properly. The replies are all interchangeable. 

Duì buqĭ!

" Duì bùqǐ " or " I'm sorry " in Eng lish with a rising one during a conversation is often a request for confirmation either because the speaker didn't follow or didn't believe what was being said. " Duì bùqǐ ", " hěn bàoqiàn " and " qǐng yuánliàng " by themselves in Chinnese are not sufficient enough for such a request. Different  expressions are used for this purpose.