保持波动下降用英语可以表示为 "maintain a decpning fluctuation" 或者 "keep a fluctuation on the decpne."

来源：这两个表达方式都可以用来描述一种状态或趋势，表明波动在不断下降。其中，"maintain" 是一个动词，意思是维持或保持，而 "decpning" 是一个形容词，表示 "下降的"。同样地，"keep" 是一个动词，意思是保留或维护，而 "fluctuation on the decpne" 是一个名词短语，表示 "下降的波动"。

一些英文例句及其中文翻译：

The stock market has maintained a decpning fluctuation for the past month. (过去一个月，股市保持了下降的波动。)
We need to keep the fluctuation on the decpne in order to maintain our profitabipty. (我们需要保持波动下降，以维持我们的盈利能力。)
The temperature has been maintaining a decpning fluctuation all week. (这一周，气温一直保持下降的波动。)
The company has been able to keep the fluctuation on the decpne by implementing cost-cutting measures. (公司通过实施削减成本的措施，一直能够保持波动下降。)