clarion call       
noun [ C usually singular ]  literary uk/ˈklær.i.ən ˌkɔːl/ us/ˈkler.i.ən ˌkɑːl/
 召唤;号召
a very clear message or instruction about what action is needed
  to issue/sound a clarion call for change 吹响变革的号角 
 
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