北门之管

Explanation: Tube: the key. To place or at Defense, said military mission 　　Usage: Partial official; as object; a military fortress 　　Source: Pre Hengyu "Zuo Xi male and three years": "to tell Qin Cheng Qi Zi from saying: 'Zheng He who made me the palm of its north gate of the pipe, if the potential teacher since the country is also available. '"Du Yu Note: The" tubes, the key also. " 　　Examples: Mud City who, Foshan and the to road, ~ send Yan. ★ "San Yuan Li, Guangzhou City, engaged in historical struggle against the British Chi Square" Thesaurus:  North Gate key