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Phrase(s): I couldn’t ask you to do that.
That is a very kind offer, but I would not ask you to do it. (This is not a refusal of the offer.) • Sally: Look, if you want, I’ll drive you to the airport. Mary: Oh, Sally. I couldn’t ask you to do that. • Bill: I’ll lend you enough money to get you through the week. Sally: I couldn’t ask you to do that.
McGrawhill's American Idioms And Phrasal Verbs