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一旦 … ，就 … (once …, then …)
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Once it starts
- A forest ranger warns visitors about fires in the dry season.
- once一旦to catch fire着火，then就very很hard难to control控制。 — "Once a fire starts, it's very hard to control."
once一旦 A，then就 B = once A happens, B
- once一旦 introduces a possible event (often serious or decisive); then就 gives what follows from it.
- It can follow the subject: you你once一旦decide决定(completed / change)了，then就don't别regret it后悔.
you你once一旦decide决定了，then就don't别regret it后悔。
Complete: “Once you've decided, don't regret it.” 你____决定了，就别后悔。
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一旦 + decisive event, 就 + result.
Warnings and decisive moments
- a habit习惯once一旦formed养成，then就very很hard难to change改变。 — "Once a habit is formed, it's hard to change."
- once一旦to have / there is有news消息，I / me我then就to notify通知you你。 — "As soon as there's news, I'll let you know."
a habit习惯once一旦formed养成，then就very很hard难to change改变。
Build: “Once a habit is formed, it's hard to change.”
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一旦 A，就 B.
A possible, important event
- once一旦 is for an event that may happen and matters; for everyday "as soon as", one / a一…then就… is more natural: I / me我一到home家then就to / for / give给you你to make a telephone call打电话.
- Pair it with then就 after the subject of the result: once一旦it rains下雨，competition (sports etc)比赛then就to cancel取消.
Everyday routine: “As soon as I get home, I take a shower.” Which fits best?
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An ordinary routine takes 一…就…; 一旦 is for weighty events.
once一旦 versus if如果 and one / a一…then就…
- if如果 = if (neutral possibility).
- once一旦 = once (the moment it happens, consequences follow) — stronger and often a warning.
if如果it rains下雨，we我们then就not不go去。
一旦 often carries a warning tone.
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It stresses consequences once something happens.
Recap
- once一旦 A，(Subject) then就 B = once A happens, B (often serious).
- Everyday sequences use one / a一…then就…; neutral conditions use if如果.
Read the full reference: HSK 5 grammar — Conditional statements.
A forest ranger warns visitors about fires in the dry season. Close the examples. Say a Mandarin response, then write it in Chinese. Explain briefly in English what the lesson’s pattern adds. Compare with the model, then change one detail and try again.
This is supported productive practice. Compare meaning and structure; your answer need not copy the model. A partner or teacher must hear the spoken response to comment on pronunciation.