It is made up of the extruder, head, cooling system, tractor unit, cutting unit, discharge pipe unit etc.

由挤出机、机头、冷却装置、牵引装置、切割装置、卸管装置组成。

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Great care had to be taken with the control systems for a powered trailer because, when turning, it can push the tractor unit over.

在拖车运行时必须谨慎地操纵控制系统，否则牵引机就会被推倒。

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Compared with tradition tractor and implement unit, a self propelled machine not only has simple structure, small unit and high efficiency, but also can be used in the paddy field and special area.

自推进耕耘机械与传统的拖拉机农具机组相比，其结构简单，机组短，效率高，适合在水田和特殊地块作业。

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Mr Homer had left the handbrake off as he went to couple a tractor unit to the trailer in a sloped bay.

BBC: Nightfreight fined ?300,000 over driver death