open shortest path first

例句：

1. 1. The door is open;please enter.
   门是开着的，请进来。
2. 2. She opened the window to let fresh air in.
   她打开了窗户，让新鲜空气进来。
3. 3. The museum is open from 9 am to 5 pm every day.
   博物馆每天上午9点到下午5点开放。