underside of the piston head

例句：

1. 1. The car'sunderside is covered in scratches anddents.
   这辆车的底部布满了划痕和凹痕。
2. 2. Thescientist examined the undersideof the moon to find evidenceof life.
   科学家检查了月球的下侧，以寻找生命的证据。
3. 3. Theunderside of the table was smootherthan the top.
   桌子的下侧比上侧更光滑。