1. 一口气：in a brace of shakes 立刻 | in a breath 一口气 | in a breeze 不费力地

2. 一瞬间 齐声地, 一口气：keep one's breath (因恐惧或激动)屏息, 暂时停止呼吸 屏息以待, 非常紧张地等待着 | in a breath 一瞬间 齐声地, 一口气 | in one breath 同时, 齐声地

3. 一瞬间：in one breath 一口气; | in a breath 一瞬间; | That took his breath away. 他大吃一惊.