stiffly  
adverb uk/ˈstɪf.li/ us/ˈstɪf.li/
  (FIRM)      
  笔挺地;僵直地
straight and not bending
  The soldiers stood stiffly to attention. 士兵们笔挺地立正站着。 
   (NOT RELAXED)      
  生硬地,拘谨地
in a way that is too formal
  "I don't think that it's anything to do with you," he said stiffly. “我认为这和你一点儿关系都没有,”他生硬地说。 
   (SEVERE)      
 UK严厉地 
severely
  I wrote a stiffly worded letter of complaint to the council. 我给委员会写了一封措词强硬的投诉信。