drag unit

例句：

1. 1. The truck was pulled by a tractor unit.
   卡车被一辆拖车牵引。
2. 2. The trailer unit is designed to carry heavy loads.
   拖车单元设计用来承载重物。
3. 3. The tractor unit helped us move the heavy furniture into the new house.
   拖车单元帮助我们把沉重的家具搬到了新房子里。