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general::
Phrase(s): What’s keeping someone?
What is delaying someone? (The someone is replaced by a person’s name or a pronoun.) • Bob: Wasn’t Mary supposed to be here? Bill: I thought so. Bob: Well, what’s keeping her? Bill: How should I know? • Bill: I’ve been waiting here for an hour for Sally. Sue: What’s keeping her?
McGrawhill's American Idioms And Phrasal Verbs