grades是单数还是复数

是复数，单数是grade，意思是等级，例如：

1.Modeling of steel ball's grade based on image texture feature.基于图像纹理特征的钢球等级分类建模

2.The method assessing beef grade based on image processing was studied.研究了一种基于图像处理和支持向量机（SVM）分类的牛肉大理石花纹等级评定技术。

3.The Ceramic Tile's Automatic Grading System Design Based on Machine Vision.基于机器视觉的瓷砖自动分类系统设计。