如图，正六边形ABCDEF内接于⊙O，⊙O的半径为1，则弧AB的长为 ____.

阅读下面这首唐诗，完成小题。

海棠

郑谷

春风用意匀颜色，销得①携觞与赋诗。秾丽最宜新著雨，娇娆全在欲开时。

莫愁粉黛临窗懒，梁广②丹青点笔迟。朝醉暮吟看不足，羡他蝴蝶宿深枝。

【注】①销得：值得。②梁广：古代画家，擅画海棠。

    Hi, everyone. I'm glad to show you around our city.

Now we are standing at Qingnian Square. ____ It is the white building over there. And it's on Changqing Street. Next to the bank is a bookstore. Many people go there to buy books. Go along Changqing Street.____. It is at the end of the street. Then turn left into Hengshan Road, and our school is on the right____. We sometimes walk along Hengshan Road to go to the swimming pool after class.____ Oh, there is a small river outside the city. ____ It is great fun.

从A, B, C, D四个选项中选择恰当的句子填入文中空缺处，使内容完整，正确。