New Words：

whistle [ˈwɪsl]
n.哨子；口哨；汽笛；汽笛声
v.吹口哨；吹哨子

Sample Sentences：

Can you hear the train whistle?
The referee finally blew the whistle to stop the game.

Please whistle when you need help.
Do you know how to whistle ? You just put your lips together and blow .

referee [ˌrefəˈriː] n.裁判;裁判员

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