> For the complete documentation index, see [llms.txt](https://once-upon-a-phd.gitbook.io/once-upon-a-phd/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://once-upon-a-phd.gitbook.io/once-upon-a-phd/aurora/hui-guo-de-dan-xuan-ti.md).

# 回国的单选题

> 客舍并州已十霜，归心日夜忆咸阳。 \
> 无端更渡桑乾水，却望并州是故乡。