我从来不能对人开玩笑，因为我忍不住笑。

I can never play jokes on people because I can't ___keep ___a ___straight ___face.

在严肃的会议上，尽管演示文稿中有个有趣的错字，他不得不保持面无表情。

During the serious meeting, he had to ___keep ___a ___straight ___face despite the funny typo in the presentation.

喜剧演员的笑话太搞笑了，观众中没人能忍住不笑。

The comedian's joke was so hilarious that no one in the audience could ___keep ___a ___straight ___face.