在实验室的工作很有趣，但你必须小心。

Lab work is fun but you must be careful.

youdao

你必须小心，别伤害到你的眼睛。

You must be careful not to hurt your eyes.

youdao

当你穿过街道时，你必须小心。

When you go across the street, you must be careful.

youdao

You handle them very special in terms of being extra careful in a very high ventilation area, in hoods is how you handle them.

在使用它们的时候你需要格外小心,必须在通风条件非常好的地方，在通风柜中才行。

麻省理工公开课 - 化学原理课程节选

but you've got to be certain when you get out there. And make a positive move.

但是你在外面，你必须要小心。然后积极行动。

我使用自行车 - SpeakingMax英语口语达人

We think a lot about weight in this country, but weight is a remarkably carefully controlled parameter of a person, that is, you have to work pretty hard to gain weight or to lose weight.

我们身在一个特别关注体重的国家,然而体重是一个,需要小心地控制地人体指标,这就是说,你必须付出相当多的努力,才能增加或减少体重

耶鲁公开课 - 生物医学工程探索课程节选