track shoe width

例句：

1. 3.
   火车等的
2. 1. The police are trying to track down the thief.
   警方正在试图追踪那个小偷。
3. 2. He followed the dog's trail of breadcrumbs.
   他沿着狗留下的面包屑痕迹跟了过去。
4. 3. The scientist used a microscope to track the bacteria's movement.
   科学家用显微镜来追踪细菌的运动。