level grade between opposite gradients

例句：

1. 1. The students are at different levels of understanding the material.
   学生们对材料的理解程度各不相同。
2. 2. The company has a hierarchy of managers at different levels.
   公司有不同级别的经理人。
3. 3. The level of the river is determined by its source and flow.
   河流的水位取决于其源头和流向。