sceptic       
noun [ C ] UK (US skeptic) uk/ˈskep.tɪk/ us/ˈskep.tɪk/
 持怀疑态度的人
a person who doubts the truth or value of an idea or belief
  People say it can cure colds, but I'm a bit of a sceptic. 人们说它能治感冒,我有些怀疑。 
 to convince the sceptics 说服持怀疑态度的人 
 Synonym: doubter