data在某一个时间段固定不变：fixed in time
在一系列的时间段中转变：changes over time
持续变化的data在不同情况下:
增加：increase / raise / rise / go up ...
减少：decrease / grow down / drop / fall ...
波动：fluctuate / rebound / undulate / wave ...
稳定：remain stable / stabilize / level off ...
最常用的两种表达法：
动词 + 副词形式
形容词 + 名词形式
1. Verb+Adverb form
The number of XXX
+increase/jump/rise/decrease/drop/fall/fluctuate...
+insignificantly/significantly/slightly/suddenly/rapidly/dramatically/sharply/steeply/steadily/gradually/slowly...
+from to / between and
2. Adjective+Noun form
There was a sudden/rapid/dramatic/significant/sharp/steep/steady/gradual/slow/slight
+increase/jump/rise/decrease/drop/fall/fluctuation
+in the number of XXX from to / between and
描述稳定的data：
The number of XXX remained steady/stable from to / between and
The number of XXX stayed the same from to / between and
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