instanteneous unit-hydrograph

例句：

1. 1. The event was so sudden that everyone was caught off guard.
   这个事件来得如此突然，以至于每个人都措手不及。
2. 2.The decision was made immediately after the meeting.
   会议结束后立即做出了决定。
3. 3. The train arrived at the station in an instant.
   火车在一瞬间就到了车站。