tonelessly       
adverb  literary uk/ˈtəʊn.ləs.li/ us/ˈtoʊn.ləs.li/
 单调地,沉闷地
in a way that does not express any emotion 
  "How do you do," said Lydia tonelessly. “你好,”莉迪亚淡淡地说。 
 He saw me, apparently without surprise, and spoke tonelessly. 他看到了我,显然没有惊讶,语气平淡。 
 See: toneless
 - More examples
 - "There's nothing we can do," he told her tonelessly.
 - They start tonelessly reading the script on the screen in front of them.
 - Her daughter only opened her mouth to sing tonelessly.