She reasoned that she must have left her bag on the train.

她断定准是把包落在火车上了。

《牛津词典》

She must have left.

她肯定看见我了。

youdao

I was oddly moved by the discrepancy between what must have been Hanna's actual concerns when she left my hometown and what I had imagined and theorized at the time.

当汉娜离开我的家乡，我那时所猜想和推测的事情就是她实际所关心在意的那些事情矛盾之处感到不解。

youdao

Our first thought was that someone must have gotten into a fight with a boyfriend and that he had unceremoniously dumped whatever she had left at his house on the street.

FORBES: A (Modern) Miracle On 6th Street NW