机械师为飞机发动机订购了一个特定的零件。

The mechanic ordered a specific ___part for the aircraft engine.

在汽车后备箱里备一些必要的备用零件以备急用是明智的。

It's wise to keep essential ___spare ___parts in your car's trunk for emergencies.

幸运的是，我们手头有必要的零件，当场修好了摩托车。

Luckily, we had the necessary ___part to fix the motorcycle on the spot.