material class number

例句：

1. 1. The engineer used a material called steel to build the bridge.
   工程师使用一种叫做钢的材料建造了这座桥。
2. 2. The company uses various materials to make its products.
   这家公司使用各种材料来制作其产品。
3. 3.The scientist studied the properties of different materials.
   科学家研究了不同材料的物理性质。