in train

(of arrangements) well organized or in progress

（安排）妥当，周密；在进行中

an investigation is in train.

调查正在进行中。

in someone/thing's train (或 in the train of)

following behind someone or something

跟随（某人，某事）；随后

train of thought

the way in which someone reaches a conclusion; a line of reasoning

思路；推理过程

I failed to follow his train of thought.

我没能跟上他的思路。