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to be confused; to be flustered; to be at a loss
突然の質問にまごついてしまった。
I was flustered by the sudden question.
道に迷ってまごついている観光客がいた。
There were tourists confused because they were lost.
初めての海外出張でまごつく場面が何度もあった。
There were many occasions when I was flustered during my first overseas business trip.