The temperature fluctuations in this area are huge, with a 20-degree difference between day and night.

fluctuations 是名词 fluctuation 的复数形式，来自动词 fluctuate（波动、起伏）。fluctuate 由词根 fluct-（流动、波动）和动词后缀 -ate 组成，字面意思是"像波浪一样上下起伏"。 fluctuations 在这里指温度像波浪一样上下变化的情况，即"温度波动"。