What went through Tom's mind I can't imagine, but he did manage to keep a straight face.

汤姆心里在想什么我想像不出来，但是他确实装着一脸严肃。

《柯林斯英汉双解大词典》

We often keep a straight face or use an unsmiling expression when we're making a joke.

当我们开玩笑的时候，我们经常绷着脸或使用不笑的表情。

youdao

Judges love to keep a straight face.

法官喜欢保持一张正直的脸。

youdao

You can see that as you fill up your periodic table, it's very clear. But also we'll tell you a pneumonic device to keep that in mind, so you always remember and get the orbital energy straight.

在你们填周期表的时候，非常清楚但是我们也要告诉你们,一个策略去记住它，所以你们总是记得,并得到连续的轨道能量。

麻省理工公开课 - 化学原理课程节选

And you can use mnemonics to try to keep these straight I see the T as sort of a plus sign.

你可以使用记忆术来记清它们,我将T看成是加号。

麻省理工公开课 - 固态化学导论课程节选

He instructs runners to keep a straight upper body and a "crunch" going in their lower abdominal muscles.

NPR: Chi Runners Poised for Softer Landings

"It tickles a bit when it's applied, " Ms. Pavenooch said, leaning back and closing her eyes as she tried to keep a straight face.

WSJ: In Thailand, Those Seeking A Golden Glow Rush to the Spa

Dr Dacke had previously shown that dung beetles were able to keep a straight line by taking cues from the Sun, the Moon, and even the pattern of polarised light formed around these light sources.

BBC: Dung beetles guided by Milky Way