A progression is a gradual development from one state to another.
例句
Both drugs slow the progression of HIV, but neither cures the disease...这两种药物都可以延缓艾滋病病情发展，但是都不能治愈这种疾病。I think they saw it as a natural progression for me.我想他们认为这对我来说是顺理成章的。
N-COUNT
（事件的）一连串，一系列，连续
A progression of things is a number of things which come one after the other.
例句
...a progression of habitats from dry meadows through marshes to open water.从干燥的草地到沼泽地再到开阔的水面的一系列栖息地
英汉词典释义
n.
(事件的)连续;一系列
A progression of disagreements has led to war between those nations.一连串的不和导致那些国家之间爆发了战争。
<数>级数
Population is increasing in that country in a geometric progression.那个国家的人口正以几何级数增长。