sanguine  
adjective  formal uk/ˈsæŋ.ɡwɪn/ us/ˈsæŋ.ɡwɪn/
  (CHEERFUL)      
 乐观的,乐天的
(of someone or someone's character) positive and hoping for good things
  They are less sanguine about the prospects for peace. 他们对和平的前景不乐观。 
 See also: optimistic