of a sudden
 突然,忽然,驀然,冷不防
 Sud·den, n. An unexpected occurrence; a surprise.
 All of a sudden, On a sudden, Of a sudden, sooner than was expected; without the usual preparation; suddenly.
    How art thou lost! how on a sudden lost!   --Milton.
    He withdrew his opposition all of a sudden.   --Thackeray.
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 of a sudden
      adv : happening unexpectedly; "suddenly she felt a sharp pain in
            her side" [syn: suddenly, all of a sudden]