spare train paths

例句：

1. 1. The spare room is available for guests to use.
   空闲房间可供客人使用。
2. 2. There are spare parts in the toolbox.
   工具箱里还有备用零件。
3. 3. We need to find a way to use the spare time efficiently.
   我们需要找到一种高效利用空闲时间的方法。