https://qooah.com/2015/04/21/%e5%93%a1%e5%b7%a5%e5%9c%a8%e5%85%ac%e5%8f%b8-line-%e7%be%a4%e7%b5%84%e7%bd%b5%e8%80%81%e9%97%86%e5%a8%98-7%e4%ba%ba%e5%90%8c%e6%99%82%e8%a2%ab%e7%82%92/