换岗

换岗	huàn gǎng	to relieve a sentry / to change the guard
换	huàn	to exchange / to change (clothes etc) / to substitute / to switch / to convert (currency)
岗	gāng	variant of 冈 [gang1]
岗	gǎng	(bound form) hillock; mound / sentry post; policeman's beat / (bound form) job; post