vacillate       
verb [ I ]  disapproving uk/ˈvæs.ɪ.leɪt/ us/ˈvæs.ə.leɪt/
 踌躇;犹豫;摇摆不定
to be uncertain what to do, or to change often between two opinions
  Her mood vacillated between hope and despair. 她时而心怀希望,时而感到绝望。 
 
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