So what I'm saying here is we are specializing to a limited class of motion where the particle has a definite acceleration, a.

我在这里想说的是,我们正在专门讨论一类问题,这些问题中,质点都有一个确定的加速度a

耶鲁公开课 - 基础物理课程节选

but I do want to be a film director specializing in, like, thrillers, kind of horror.

但我希望能够成为专门拍摄惊险或恐怖片的导演。

要成为导演 - SpeakingMax英语口语达人