通常用来形容难度逐渐增加的英语表达是 "progressive difficulty"。这个表达是由 "progressive"（意思是逐步的、进步的）和 "difficulty"（意思是困难）构成的。
下面是一些例句：
The Engpsh lessons are designed with a progressive difficulty, starting with basic grammar and vocabulary and gradually introducing more complex concepts.
The reading passage has a progressive difficulty, with the first few paragraphs being relatively easy and the last few being more challenging.
The math problems in this book have a progressive difficulty, so students can gradually build their skills and confidence.
例句翻译：
这套英语课程是从基本语法和词汇开始，逐渐增加难度设计的。
这篇阅读文章的难度是逐渐增加的，前几段相对较简单，后几段会更具挑战性。
这本数学书的题目难度是逐渐增加的，所以学生们可以逐步建立自己的技能和信心。
下面是一些例句：
The Engpsh lessons are designed with a progressive difficulty, starting with basic grammar and vocabulary and gradually introducing more complex concepts.
The reading passage has a progressive difficulty, with the first few paragraphs being relatively easy and the last few being more challenging.
The math problems in this book have a progressive difficulty, so students can gradually build their skills and confidence.
例句翻译：
这套英语课程是从基本语法和词汇开始，逐渐增加难度设计的。
这篇阅读文章的难度是逐渐增加的，前几段相对较简单，后几段会更具挑战性。
这本数学书的题目难度是逐渐增加的，所以学生们可以逐步建立自己的技能和信心。