the sound that people make when they want somebody to repeat something (請對方再說一遍)嗯,什麽 the sound that people make when they want somebody to agree or reply (征求對方同意或答複)是嗎,好嗎,嗯 the sound people make when they are surprised (表示驚奇)啊
Word Originnatural utterance: first recorded in English in the mid 16th cent.