valve reversal的用法和樣例：
例句
- When the next reversal occurs, the several generations of scientists who study it will know much more about the effects.
當下一次倒轉發生時，從事這項研究的幾代科學家將對有關的效應知道得更多。 - In order for a reversal to take place there must be a brief time during which the field is non-existent.
為了發生一次倒轉，必須有一個很短的時間沒有磁場存在。
