問題図 https://hirakawatblog.com/%e7%89%a9%e7%90%86%e5%9f%ba%e7%a4%8e%e2%91%ad%e3%80%80%e9%81%8b%e5%8b%95%e6%96%b9%e7%a8%8b%e5%bc%8f%e2%91%a1%ef%bc%88%e5%bf%9c%e7%94%a8%e7%b7%a8%ef%bc%89%e3%80%80%ef%bd%9e%ef%bc%92%e7%89%a9%e4%bd%93/%e5%95%8f%e9%a1%8c%e5%9b%b3