graded series

例句：

1. 1. The company has introduced a new graded series of products for its customers.
   该公司为顾客推出了新的分级系列产品。
2. 2. In the field of education, there are different graded series of textbooks available for students to choose from.
   在教育领域，学生可以选择不同级别的教材。
3. 3. The graded series of courses is designed to help students improve their skills and knowledge in a systematic way.
   这个分级课程系列旨在帮助学生系统地提高他们的技能和知识。