快速答案
acabar de＋不定式表示刚刚完成；deixar de＋不定式表示停止或未做。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
acabar de
to have just done
Use acabar de for an action completed very recently.
deixar de
to stop or fail to do
Use deixar de for ending a habit or not carrying out an expected action.
如何选择
- acabar de: Choose acabar de if the sentence points to an action completed very recently.
- deixar de: Choose deixar de if the sentence points to ending a habit or not carrying out an expected action.
例句
Acabei de chegar.
I have just arrived.
Ela deixou de fumar no ano passado.
She stopped smoking last year.
常见误区
The small preposition changes the timeline completely: acabei de trabalhar means I just worked; deixei de trabalhar means I stopped working.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 acabar de，一次用 deixar de。如果两个版本都可以，说明意思怎样变化。