As Soon As (一...就)

一...就 expresses that one action follows another immediately or inevitably. "As soon as I got home, it started raining" — 我一到家，就下雨了. The 一 marks the trigger event, and 就 marks the immediate result.

This pattern can describe one-time events in the past (我一看到她就笑了 — As soon as I saw her, I laughed), habitual patterns (他一紧张就说不出话来 — Whenever he gets nervous, he can't speak), or general truths (一到冬天就很冷 — As soon as winter comes, it gets cold).

The subjects of the two clauses can be the same or different. When they are the same, the subject usually appears only once at the beginning: 他一回家就看电视. When different, each clause has its own subject: 老师一说，学生们就明白了.

A common extension is using 一...就 to describe someone's quick ability or habit: 她一学就会 (She picks it up as soon as she studies it). This pattern feels very natural in Chinese and is used constantly in daily conversation.