preheating circuit

例句：

1. 1. The heating system in the factory needs to be preheated before it starts working.
   工厂里的加热系统在开始工作前需要预热。
2. 2. The engineer designed a new preheating circuit for the machine.
   工程师为机器设计了一个新的预热电路。
3. 3. The preheating circuit was responsible for warming up the engine before starting the car.
   预热电路负责在启动汽车之前加热发动机。