straight face 板着脸，不动声色，一本正经的样子

　　It was difficult to keep a straight face when I heard his joke.

　　听完他的笑话，很难板着脸不笑。

　　My father never laughs. What he gives us is always a straight face.

　　父亲从来不笑。他面对我们时候总板着个脸。

　　疯狂练习吧！