小齿轮

例句：

1. 1. The car needs a new spark plug to keep it running smoothly.
   这辆车需要更换火花塞才能顺畅运行。
2. 2. The engineer replaced the worn-out gear with a new one.
   工程师用一个新的替换了磨损的齿轮。
3. 3. The old clock needed a small gear to keep it ticking.
   旧时钟需要一个小齿轮来保持其走动。