magnetic return path

例句：

1. 1.The magnetized metal strips attract each other.
   被磁化的金属条相互吸引。
2. 2.Magnetic fields are used in many scientific experiments.
   磁场在许多科学实验中被使用。
3. 3.The scientist discovered a new type of magnet that could be used to control the flow of oil.
   科学家发现了一种新型磁铁，可以用来控制石油的流动。