physical atomic weight

例句：

1. 1.The physics teacher explained the concept of gravity to us.
   物理老师向我们解释了重力的概念。
2. 2.The material was so strong that it could not be easily broken.
   这种材料非常坚固，不容易被打破。
3. 3. The tangible evidence of their love is the rings they exchanged.
   他们爱情的有形证据是他们交换的戒指。