shaft of metacarpal bone

例句：

1. 1. The car's engine is located in the centerof the engine block.
   汽车的发动机位于发动机缸体中心。
2. 2. The tree'strunk is a sturdy shaft that supports thebranches.
   这棵树的主干是一个结实的轴，支撑着树枝。
3. 3. Themachine has a long shaftthat can be used for variouspurposes.
   这台机器有一个长轴，可以用于各种用途。